Method of forming a coating layer on the surface of a molded product within a mold

ABSTRACT

An in-mold coating apparatus providing a mold having a specifically formed auxiliary cavity and an in-mold coating formation method which employs said mold, so that it is possible to prevent a coating material from leaking out of the mold, thereby shortening the molding formation cycle, and making it possible to manufacture a molded product having a stabilized quality. In addition, by using a mold having a specifically shaped sub-cavity, there is provided a still further in-mold coating formation method which can keep mold temperature at a relatively low value, cause the coating material to cure at a predetermined temperature and within a predetermined time period thereby shortening the molding formation cycle, improving the productivity, improving the physical properties of a coating layer, thus obtaining a good molded product.

This application is a divisional application of prior application Ser.No. 10/030,126 filed on Jan. 24, 2002, which is a National Stage ofInternational Application No. PCT/JP00/04779 filed Jul. 17, 2000 nowabandoned.

TECHNICAL FIELD

The present invention relates to an in-mold coating formation method inwhich a thermoplastic resin molded product is molded in a mold,subsequently a coating material is injected into the mold to form acoating layer on the surface of thus obtained thermoplastic resin moldedproduct. This invention also relates to an in-mold coating formationapparatus for use in the in-mold coating formation method for forming acoating layer on the surface of a molded product within a mold. Thisinvention further relates to an in-mold coating formation mold for usein the in-mold coating formation apparatus and also relates to anin-mold coating formation method which utilizes the in-mold coatingformation mold formed for use in the in-mold coating formationapparatus.

BACKGROUND ART

There have been proposed in-mold coating formation methods, aiming atimproving a quality of products by adding some additional values such asdecorative effects on some thermoplastic resin molded products oftenused in automobiles and house hold electric apparatus or devices or usedas construction materials, or aiming at reducing the production cost byomission of certain steps in molding process thereof; said in-moldcoating formation method comprises the steps of injecting a coatingmaterial into a space between the surface of a thermoplastic resinmolded product formed in a mold and the internal surface of the cavityof the mold, and then curing the coating material within the mold so asto obtain an integrally formed molded resin product on whose surface acoating layer is adhered. In particular, those methods have been used tocertain extent in the production of the thermoplastic resin productsused as various parts in an automobile vehicle whose requirements as tothe appearance and the quality are quite severe. These parts may includea bumper, a sideview mirror cover, a fender, a door panel, a back doorpanel, an over fender, a door handle, a side garnish, a side protector,a wheel cap, including a side cover and a cowl for use in a motorcycle.

There have been known several in-mold coating formation methods, such asthose disclosed in U.S. Pat. No. 4,076,788, U.S. Pat. No. 4,081,578,U.S. Pat. No. 4,331,735, U.S. Pat. No. 4,366,109, U.S. Pat. No.4,668,460, JP-A-5-301251, JP-A-5-318527, and JP-A-8-142119.

In the case of methods disclosed therein, there are some prescriptionsas to the mold closing force at the time when a coating material isinjected into the space between the inner surface of the mold and thethermoplastic resin molded product after formation of the moldedproducts from the thermoplastic resin material for molding within themold, the injection pressure of the coating material, and a moldclearance. However, there is almost no attention to be paid to timerequired for injecting a coating material and the time required forcompleting the reclosing of the mold after the coating material has beeninjected into the mold.

Namely, a thermosetting material starts its solidification by virtue ofa heat of the inner surface of the mold and a heat of the thermoplasticresin material immediately after it is injected into a mold. A curingspeed thereof will vary from case to case, depending upon variousconditions such as the sort of a coating material, the temperature of amold, the temperature of a thermoplastic resin material, and the like.

If the coating material injection time is too short, pigment componentscontained in a coating material will be undesirably separated from eachother in the coating material or some weld lines will be undesirablyformed. On the other hand, if the coating material injection time laststoo long, an end portion of the molded product is often not coated sincea flowability of a coating material will decrease with the progress ofthe solidification of the coating material, and/or some wrinkles andcracks will be formed in a coating layer.

Moreover, if an operation time until the completion of the reclosing ofthe mold is too long, the coating material will undergo an undesired gelwith the progress of its solidification, resulting in a decrease in itsflowability and hence making it difficult for a coating material tocover an entire molded resin product including its end portions, and/ora pressure needed in reclosing the mold will also be applied to thecoating material during its gel, causing some wrinkles and cracks in thecured coating layer formed on the surface of the molded resin product.On the other hand, if an operation time before the completion of thereclosing of the mold is too short, pigment components contained in thecoating material will be undesirably separated from each other in thecoating material, and some weld lines will be undesirably formed, makingit impossible to produce molded resin products having a uniformappearance. Further, in the case of molded products having ribs andbosses, if a pressure for reclosing the mold is not made proper, somedefects such as sinks and humps (which are in fact tubercles formed onthe surface of thick portions of the molded product) will be formed inthe molded products.

For this reason, firstly, it is earnestly desired at the present time toestablish an improved in-mold coating formation method which requiresthat after a thermoplastic resin product has been formed within a mold,a coating material is injected into the mold to form a coating layer onthe surface of the molded resin product, with the coating formationprocess being carried out without forming any wrinkles, cracks, mottles,and weld lines in the cured coating layer, thereby obtaining moldedresin products having a coating layer of a high quality.

Further, the above mentioned in-mold coating formation method(hereinafter it is referred to sometimes as IMC method) has attracted aconsiderable attention from people in the art and has been considered tobe very effective to serve as a substitution for a conventional spraycoating technique; this is because there is a tendency that officialrestrictions for controlling the discharge of harmful organic compoundsfrom various factories into surrounding atmosphere become more and moresevere, and from the viewpoints that serious attention should be paid tothe health protection of workers working in the factories under thecircumstances that environment problems have attracted big concerns moreand more during recent years.

Incidentally, the above mentioned IMC method was initially developedmainly for use in manufacturing a molded resin product from athermosetting resin such as SMC or BMC. However, in recent years,attempts have been made to apply an IMC method to form an thermoplasticresin product. For example, as is disclosed in JP-A-5-301251, there hasbeen proposed a method comprising injecting a coating material of athermosetting resin onto the surface at the injection inlet of a moldedresin product by altering a closing force of the mold, or maintaining aclosing force of the mold at a constant level, under a condition wherethe surface temperature of a resin is equal to or higher than the curingtemperature of a coating material, and opening the mold after thecoating material has been cured.

However, it is difficult to design optimum molding conditions for aformed coating layer to obtain a good appearance and a good adhesionstrength, compared with an IMC method for a thermosetting resin from thefollowing reasons or the like: a mold temperature in an IMC method for athermoplastic resin will be fairly lower than that in an IMC method fora thermosetting resin; and, in the case of a coating material for athermoplastic resin in an IMC method, it is required to have a curingproperty capable of curing at a temperature lower than a coatingmaterial for a thermosetting resin does.

Further, a conventional injection molding machine is designed only formolding a resin product having a predetermined shape, but not forcarrying out an IMC method. Therefore, one may point out the point, asone of reasons making it difficult to use an IMC method of athermoplastic resin, that the conventional injection molding machine isdesigned not so as to carry out the controls of the position of a moldand the mold closing force with a high precision and a high response.That is, it is impossible to spread a coating material sufficientlywithin the cavity of a mold after the injection thereof into the mold,or it is extremely difficult to obtain a uniform coating layer since aninjected coating material starts to cure partially soon after it hasbeen injected into the mold. Accordingly, even if in a case where themethod disclosed in JP-A-5-301251 is used, it is difficult to controlthe curing condition for curing the coating material, as far as aconventional injection molding machine is used whose control operationfor controlling the mold closing force and mold position is slow, hencerendering it difficult to ensure a high productivity.

Therefore, in order to improve the above mentioned situation,JP-A-6-254886 has proposed an attempt to adjust conditions for an IMCmethod by giving a predetermined amount of opening of the mold. However,in the case of the IMC apparatus for this method, there is employed ameans for stopping at a position capable of ensuring a predeterminedamount of opening of the mold as a result of the interaction between twosets of the driving means installed in the opposite direction eachother, by installing another driving means for driving the mold in theopposite site in addition to a driving means for effecting the openingor closing of a mold. Accordingly, the control system thereof is complexand it is difficult to ensure a high response. This brings inherently aproblem that it is impossible to shorten an operation time which lastsuntil the mold arrives at its predetermined stop position.

Moreover, with regard to an injection molding machine of a hydraulicdirect press type which has been used in prior art, since a mold closingforce control for controlling a mold pressing force and a mold openingamount control for controlling the mold position are effected bydifferent control systems, although very slightly, a time lag will occurwhen the mold position control is changed over to the mold closing forcecontrol, making it impossible for the mold to be suitable for acontinuous operation. As a result, with regard to an IMC method that iscarried out in an injection molding machine of a hydraulic direct presstype, at the time when the operation of the mold is interrupted, someflow lines will occur in coating material flowing areas within thecavity of a mold. Namely, there has been existing a problem that theconventional injection molding machine of the hydraulic direct presstype is not suitable for carrying out an in-mold coating formationmethod which requires that the mold closing force and the mold openingamount be controlled continuously. In conclusion, there was only a lowyield even if people tried their best to manufacture a thermoplasticresin molded product coated with a properly formed coating layer.

Because of the reasons stated in the above, it has been stronglydemanded to develop an improved in-mold coating formation method and animproved in-mold coating formation apparatus, which are able to controla mold closing force and a mold opening amount with a high precision anda high response even under a condition where the mold closing force andthe mold opening amount are required to be continuously changed, so asto greatly enlarge a selectable range for selecting suitablemanufacturing conditions for carrying out an IMC method for athermoplastic resin so as to produce an integrally formed resin productbeing excellent in the appearance and the adhesion strength of itscoating layer.

However, as discussed in the above, although the conventional IMC methodis utilized partly only for the manufacture of a molded product from athermosetting resin such as SMC resin and BMC resin, this method hasbeen not utilized widely yet for an injection molding of a thermoplasticresin. A key reason for this, one may point out one problem that thecoating material often leaks out of the mold. In particular, since it isnot easy to carry out an operation to remove coating material leakedfrom the mold, and since the injection molding machine has to be stoppedat every time when the coating material is leaked, a cycle for theformation of a molded product will become too long, hence resulting in alow productivity. Moreover, since the leaked coating material can forman additional load during a process in which a mold is being closed, apredetermined mold closing force will become insufficient, causing aproblem that the leaked coating material will adhere to a molded productto be produced in a next production cycle, thus making it difficult toconstantly maintain a good quality for molded resin products.

In order to cope with the leakage problem of a coating material,JP-A-6-328505 has proposed an improved mold for use in an injectionmolding process, in which the shear edge portion(s) is(are) formed so asto prevent a coating material from leaking out the mold, while utilizingparting surfaces. However, since it is still impossible to completelyprevent a leakage of a coating material even if this type of the mold isemployed, an internal space is required to be formed within the mold forstoring the leaked coating material. Consequently, since it is necessaryto perform an operation to remove the coating material accumulated inthe shear edge portion(s) and this internal space, it is considered thatthis is the cause of reducing the productivity.

In addition, there is proposed in JP-A-9-48044 a mold having partingsurfaces wherein an auxiliary cavity is arranged in parallel with theparting surfaces in order to prevent a possible leakage of a coatingmaterial. However, in the case that this type of the mold is used, thecoating material can be injected into the mold only under the statewhere the mold is closed.

Further, the said publication also discloses another mold having groovesformed within the auxiliary cavity. However, such grooves are requiredto have a thickness of 0.1 to 0.5 mm not so as to make a coatingmaterial leaked into a clearance (a gap formed between a groove-formingrib area and a mold cavity surface) formed due to a curing shrinkage ofa resin material used for molding. One may not allow, however, to have asufficient height in the case of the grooves having such a thickness dueto the requirements in the strength of the mold movement. Consequently,if a coating material is injected into the mold by opening it at apredetermined opening amount, a coating material will be leaked. On theother hand, even if the grooves are made higher than the opening amountof the mold, there is still a possibility that the grooves are notdurable enough in their strength against an injection pressure ofcoating material.

Moreover, there is disclosed in JP-A-9-52262 a mold being formed with arecess portion located surrounding an opening portion (sprue portion) ofa molten resin injecting section, so as to prevent a coating materialfrom flowing into the sprue portion. However, similar to an inventiondisclosed in JP-A-9-48044, when a coating material is injected into amold opening it at a predetermined amount, it is considered that theeffect of preventing a possible leakage of a coating material is small.

That is, thirdly, there is a strongly desire to provide an in-moldcoating formation mold which is capable of preventing a coating materialfrom leaking out of the mold and an in-mold coating formation methodusing the same, so as to shorten the formation cycle of each moldedproduct and at the same time to stabilize the product quality.

Moreover, in an IMC method for a thermosetting resin, a mold to be usedis mainly a shear edge type mold. This is because the coating materialis prevented from flowing out of the mold cavity at the time ofinjecting subsequently the coating material since the thermosettingresin will exhibit so good flowability at the early stage of the moldingthat the resin material can fill the clearance within the shear edgeportion(s).

On the other hand, in an IMC method for a thermoplastic resin, althoughthere has been used an injection molding process suitable for molding athermoplastic resin, most of the molds for use in the method are flatparting type molds not having shear edge portions.

However, in the case when this flat parting type mold is used, partingsurfaces of the mold are not sealed by a previously injected resin to beused for molding, so that the sealing of a coating material at the endportions of a mold cavity is not sufficient. As a result, since thecoating material will leak from the mold cavity, one may not keep thecoating material at end portion of the mold under a high pressure.Accordingly, there has been such a problem that the quality of thecoating layer of an integrally formed molded product is injured. This isbecause the adhesion strength between the coating material and anthermoplastic resin molded product is reduced due to the insufficientpressure at the vicinity of the end portions of the integrally formedmolded resin product, in the case of the IMC method for a thermoplasticresin by using a conventional flat parting mold as mentioned above.

In order to solve the above problem associated with the above IMC methodfor a thermoplastic resin, there has been employed such a practice thatthere is used a special coating material containing a component havingan excellent affinity with a thermoplastic resin, or a modified specialgrade resin, so as to cover the insufficiency in the adhesion strengthof a coating material. However, there has been a problem that thedevelopment of a special coating material and a special grade resin notonly needs a long time and a considerable expense. Additionally, it hasbeen found to be impossible to completely remove the insufficiency ofthe adhesion strength of a coating material.

In addition, since a conventional hydraulic direct press type injectionmolding machine using a hydraulic cylinder has not been so designed tobe able to carry out the IMC method, it is difficult to perform adelicate position control on a mold. Further, since the driving speed ofthe mold is slow, it is difficult to control operating conditionslasting from the injection of the coating material to the curingthereof. Thus, the above-mentioned may be considered to be one of thefactors making it difficult to molding of a thermoplastic resin by theIMC method.

That is, fourthly, it has been demanded to provide an IMC method whichis capable of producing an integrally formed molded resin product havingan improved adhesion strength between a coating layer and the moldedresin product formed by a thermoplastic resin material.

As discussed in the above, in recent years there have been triedattempts so as to use an IMC method for molding a thermoplastic resinmaterial. For example, JP-A-5-301251 has proposed a method whichcomprises injecting a thermo-setting coating material on to the surfacesto be coated by changing a mold closing force, or holding the same moldclosing force, under a condition where a resin surface temperature and amold temperature are all equal to or higher than the curing point of acoating material, opening the mold once the coating material has beencured.

Further, JP-A-5-301251 has disclosed the use of an IMC method which issimilar to a common injection molding process, involving a step ofinjecting a molten resin at a temperature of 280° C. into the cavity ofa mold, and using a coating material whose curing temperature is atabout 130° C. after the mold temperature is made to 130° C. In fact, thecuring temperature of a coating material varies one from anotherdepending upon the nature of each coating material. However, if the moldhas to be set at a temperature which is equal to or higher than thecuring temperature of a coating material, the heating of the mold and aheating means will become too large in their scales, resulting in a highequipment cost and a high equipment running cost. Further, if a mold isused at such a high temperature, there is a fear that the mold willquickly become deteriorated in its quality.

Particularly, as in the method disclosed in JP-A-5-301251, if a mold isat a high temperature, a thermoplastic resin molded product will be inits soft state. Accordingly, it is necessary that a molded resin productbe taken out from the mold only after it has been cooled to atemperature at which its shape can be exactly maintained. In thismanner, if the resin molding process involves repeated cooling andheating treatments, a time period needed for one cycle molding processwill become too long, hence resulting in a low productivity. In view ofthe above various problems, not only it is difficult to expect a highproductivity by using the method disclosed in JP-A-5-301251, but alsoone may expect a high cost from equipment-wise and production step-wise.

In order to improve a low productivity resulted from the use of a hightemperature mold, such as in the case which involves the use of aconventional method disclosed in JP-A-5-301251, the actual situation atpresent remains such a condition that one should set the surfacetemperature of a mold for use in the IMC method, in view of the moldingformation cycle and the molding capability, at a value which is lowerthan the curing temperature of a commonly used coating material.

However, in the case of the coating layer formed under the conditionsincapable of satisfying the predetermined requirements for curing, thereis a possibility that it is difficult to obtain some desired physicalproperties. Further, coating materials capable of using are oftenlimited. For these reasons, in view of handling coating materials andphysical properties of a coating layer, it is preferred that a coatingmaterial for use in an IMC method should have a high curing temperature.However, there is such a situation that it is unavoidable to sacrificethe desired physical properties of a coating layer if a highproductivity is considered to be important; and, on the other hand, itis unavoidable to sacrifice the high productivity in order to form acoating layer having sufficient physical properties, in the case of theconventional IMC method for a thermoplastic resin material.

That is, fifthly, it is the present situation that there is a strongdesire to provide an IMC method for the thermoplastic resin materialwhich is capable of improving the physical properties of coating layerobtainable with shortening in the mold formation cycle so as to improvethe productivity, as a consequence of setting a mold temperature at avalue which is lower than a curing temperature of a thermosettingcoating material, and being capable of curing the coating material at apredetermined temperature and within a predetermined time period.

DISCLOSURE OF INVENTION

The present inventors, after their hard and diligent researches forsolving the above-described problems, have found that the followingmethod and apparatus can be used to achieve their purposes. Firstly,there is provided an in-mold coating formation method, wherein the moldis opened at a predetermined interval after a thermoplastic resinmaterial is subjected to molding within a mold, a predetermined amountof a coating material is injected into a space formed between thesurface of the thermoplastic resin molded product and the internalsurface of the mold cavity of the mold by using a coating materialinjection device, the mold is reclosed upon the completion of injectionof the coating material, the injected coating material is allowed tocure within the mold so as to obtain an integrally formed molded producthaving a coating layer tightly adhered to the surface of thethermoplastic resin molded product, characterized in that: (1) injectionof a coating material is performed only after a time period has passedwhich is necessary for the surface of the thermoplastic resin moldedproduct to be cured to such an extent that said surface can withstand aninjection pressure of the coating material and a flowing pressure of thesame;

(2) an injection time of the coating material is set to be within arange of 0.10 t₁ to 0.99 t₁ when a gel time of the coating material atthe temperature of the mold is defined as t₁;

(3) a time period from the beginning of injection of the coatingmaterial to its spreading through the interior of the mold by reclosureof the mold is set to be within a rang of 0.20 t₁ to 1.10 t₁ wherein t₁is the same meaning as defined in the above.

Secondly, there is provided another in-mold coating formation methodwherein the mold is opened to form a predetermined interval after athermoplastic resin material is subjected to molding within a mold, apredetermined amount of a coating material is injected into a spaceformed between the surface of the thermoplastic resin molded product andthe internal surface of the mold cavity of the mold by using a coatingmaterial injection device, the mold is reclosed upon the completion ofinjection of the coating material, the injected coating material isallowed to cure within the mold so as to obtain an integrally formedmolded product having a coating layer tightly adhered to the surface ofthe thermoplastic resin molded product, characterized in that: a strokeof a hydraulic cylinder for providing a driving force to close a mold ina toggle type injection molding machine, or a stroke of a ball screw forproviding a driving force to close a mold in a toggle type electricinjection molding machine, is subjected to a feedback control which isperformed by using a mold closing servo valve or a servo motor, therebyeffecting a drive control using a preset mold opening amount changingpattern and a preset mold closing force changing pattern.

In the in-mold coating formation method according to the above secondaspect of the present invention, it is preferred that an in-moldpressure of the coating material injected in the mold be subjected to afeedback control using a mold closing servo valve or a servo motor,thereby effecting a drive control using a preset changing pattern. It isalso preferred that various command signals representing a start of themeasurement of the coating material injection device, a start of themold opening of an injection molding machine, a start of the injectionof the coating material injection device, and a start of the moldreclosing movement of the injection molding machine, be sent andreceived so as to effect an interlock between the injection moldingmachine and the coating material injection device. Further, it ispreferred that an in-mold pressure of the coating material injected inthe mold is increased soon after the completion of the coating material,and is then changed through many steps with the passing of time so thatthe pressure is gradually reduced, thereby controlling the thickness ofthe coating layer and the curing condition of the coating material.

Further, according to the second aspect of the present invention thereis provided an in-mold coating formation apparatus, wherein after athermoplastic resin molded product has been formed within a mold, themold is opened to form a predetermined interval, a predetermined amountof a coating material is injected into a space formed between thesurface of the thermoplastic resin molded product and the internalsurface of the mold cavity of the mold by using a coating materialinjection device, the mold is reclosed upon the completion of injectionof the coating material, the injected coating material is allowed tocure within the mold so as to obtain an integrally formed molded producthaving a coating layer tightly adhered to the surface of thethermoplastic resin molded product, characterized in that the apparatuscomprises:

a mold closing servo valve for controlling a flow rate and a pressure ofa working oil being supplied to a mold closing hydraulic cylinder in atoggle type injection molding machine; a stroke sensor for detecting thestroke of the hydraulic cylinder; a mold opening amount sensor fordetecting the mold opening amount of the mold; a mold closing forcesensor for detecting a mold closing force of the mold; a coatingmaterial pressure sensor for detecting an in-mold pressure of thecoating material injected in the mold; a coating material injectiondevice for injecting the coating material; a mold closing conditionsetting section for setting and inputting the mold's mold opening amountchanging pattern and its mold closing force changing pattern, and thecoating material's in-mold pressure changing pattern; injection devicecontrol section for receiving a command signal fed from the mold closingcondition setting section so as to drive and control the coatingmaterial injection device; a changing pattern storing section capable ofstoring a correlation between a stroke of the hydraulic cylinderdetected by the stroke sensor and a mold opening amount detected by themold opening amount sensor, and another correlation between a stroke ofthe hydraulic cylinder detected by the stroke sensor and a mold closingforce detected by the mold closing force sensor, also capable ofconverting a mold opening amount changing pattern and a mold closingforce changing pattern (both of which have been set in advance in themold closing condition setting section) into stroke changing patterns ofrespective hydraulic cylinders; a mold closing control section which isprovided to cause the mold closing servo valve to perform a feedbackcontrol in accordance with a stroke changing pattern of the hydrauliccylinder and an in-mold pressure changing pattern of the coatingmaterial.

In fact, the in-mold coating formation apparatus is so formed that thetoggle type injection molding machine may be replaced by a toggle typeelectric injection molding machine, the mold closing hydraulic cylindermay be replaced by a mold closing ball screw, the mold closing servovalve may be replaced by a servo motor.

Thirdly, according to the present invention, there are provided anin-mold coating formation mold and an IMC method using the mold. Thein-mold coating formation mold is equipped with a coating materialinjection device that is provided for injecting a coating material intothe mold cavity in order that a coating layer can be formed on thesurface of a thermoplastic resin molded product formed by virtue of themold, and which is also equipped with an auxiliary cavity communicatedwith the mold cavity of the mold through the entire circumferencethereof.

As a mold which can be used in an example according to a third aspect ofthe present invention, it is allowed to use a shear edge type moldhaving a shear edge portion, and an auxiliary cavity formed in the shearedge portion. It is also allowed to use another type of mold having sucha parting structure that it includes parting surfaces connected with oneend of the auxiliary cavity as viewed in its longitudinal direction.

Namely, as the above described molds, it is allowed to use such anin-mold coating formation mold which is equipped with a coating materialinjection device for injecting a coating material into a mold cavity inorder that a coating layer can be formed on the surface of athermoplastic resin molded product within the mold, characterized inthat:

an auxiliary cavity extending in the opening and closing direction ofthe mold is formed which is communicated with the mold cavity of themold through the entire circumference thereof, the auxiliary cavity hasa thickness of 0.1 to 2 mm and a length of 0.5 to 30 mm. In addition, itis preferred that a heater be provided for heating a cavity surface ofthe auxiliary cavity, said cavity surface being on the coating materialinjection side.

Moreover, according to the third aspect of the present invention thereis provided a further in-mold coating formation method, wherein anin-mold coating formation mold is used which is equipped with a coatingmaterial injection device that is provided for injecting a coatingmaterial into the mold cavity in order that a coating layer can beformed on the surface of a thermoplastic resin molded product formed byvirtue of the mold, and which is also equipped with an auxiliary cavitycommunicated with the mold cavity of the mold through the entirecircumference thereof, characterized in that: an auxiliary molded bodyis formed by a resin to be used for molding injected into the auxiliarycavity, a small gap is formed because of a small shrinkage of theauxiliary molded body so that the small gap is located between theauxiliary molded body and the internal surface of the auxiliary cavity,said gap being used in preventing the coating material from flowing outof the mold.

Here, it is preferred that the temperature of the cavity surface on thecoating material injection side of the auxiliary cavity is kept higherthan other parts of the mold, the coating material spread from the moldcavity surface is cured in the auxiliary cavity, thereby preventing thecoating material from flowing out of the mold. Further, it is preferredto use a higher mold closing force than a mold closing force for use inthe case not involving an auxiliary cavity, and to fill the auxiliarycavity with a resin under a filling pressure which is higher than usual.

Fourthly, according to the present invention there is provided anin-mold coating formation method, wherein after a thermoplastic resinmolded product has been formed within a mold, the mold is opened to forma predetermined interval, a predetermined amount of a coating materialis injected into a space formed between the surface of the thermoplasticresin molded product and the internal surface of the mold cavity of themold by using a coating material injection device, the mold is reclosedupon the completion of injection of the coating material, the injectedcoating material is allowed to cure within the mold so as to obtain anintegrally formed molded product having a coating layer tightly adheredto the surface of the thermoplastic resin molded product, characterizedin that: after a thermoplastic resin molded product has been formed, themold is opened to form a predetermined interval, a predetermined amountof a coating material is injected into a space formed between thesurface of the thermoplastic resin molded product and the internalsurface of the mold cavity of the mold by using a coating materialinjection device, the mold is then closed upon the completion ofinjection of the coating material; an in-mold pressure of the coatingmaterial is controlled such that said pressure will arrive at apredetermined value which is 5 MPa or higher in a zone where the in-moldpressure of the coating material applied to the thermoplastic resinmolded product becomes lowest. Preferably, the above control isperformed in a manner such that the in-mold pressure will be in a rangeof 5 MPa to 15 MPa, while at the same time the coating material iscaused to flow over the entire surface of the thermoplastic resin moldedproduct so as to tightly cover the same. After that, the in-moldpressure of the coating material is controlled such that said pressurewill arrive at a predetermined value which is 0.5 MPa or higher,preferably 0.5 MPa to 2.0 MPa, in a zone where the thermoplastic resinmolded product receives the lowest pressure within the mold.

In the in-mold coating formation method according to a fourth aspect ofthe present invention, a sub-cavity is formed which is communicated withthe mold cavity, a groove portion is formed which is communicated withthe sub-cavity. Further, according to the in-mold coating formationmethod of the present invention, it is preferred to use a toggle typeinjection molding machine or a toggle type electric injection moldingmachine.

Fifthly, according to a fifth aspect of the present invention, there isprovided a still further in-mold coating formation method, wherein aftera thermoplastic resin molded product has been formed within a mold, themold is opened to form a predetermined interval therebetween, a coatingmaterial injection device is then used to inject a predetermined amountof coating material into a space formed between the surface of thethermoplastic resin molded product and the internal surface of the moldcavity of the mold, the mold is reclosed upon the completion ofinjection of the coating material, the injected coating material isallowed to cure within the mold so as to obtain an integrally formedmolded product having a coating layer tightly adhered to the surface ofthe thermoplastic resin molded product, characterized in that a coatingmaterial is injected under a condition where the surface temperature ofthe thermoplastic resin molded product is higher than the curingtemperature of the coating material, and the temperature of the mold onthe mold cavity side is lower than the curing temperature of the coatingmaterial.

Further, according to this aspect of the present invention there isprovided a still further in-mold coating formation method, wherein aftera thermoplastic resin molded product has been formed within a mold, themold is opened to form a predetermined interval therebetween, a coatingmaterial injection device is then used to inject a predetermined amountof coating material into a space formed between the surface of thethermoplastic resin molded product and the internal surface of the moldcavity of the mold, the mold is reclosed upon the completion ofinjection of the coating material, the injected coating material isallowed to cure within the mold so as to obtain an integrally formedmolded product having a coating layer tightly adhered to the surface ofthe thermoplastic resin molded product, characterized in that: when thesurface of the thermoplastic resin molded product has been cured, themold is opened at a predetermined interval, a heat diffusion from thesurface of the thermoplastic resin molded product to the mold isprohibited, after the surface temperature of the thermoplastic resinmolded product has been increased to a value which is equal to or higherthan the curing temperature of the coating material because of an amountof heat held within the thermoplastic resin molded product, the coatingmaterial is injected.

When carrying out the in-mold coating formation method according to thefifth aspect of the present invention, it is preferred to use aninjection molding machine having an excellent mold driving capabilityand an excellent positioning capability, and it is also preferred to useeither a toggle type injection molding machine or a toggle type electricinjection molding machine.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory view schematically indicating an examplerepresenting an in-mold coating formation apparatus that can be suitablyused in one example of the present invention.

FIG. 2 is a flow chart indicating a molding processes according toexample 1 and example 2, both of which can be carried out with the useof the in-mold coating formation apparatus shown in FIG. 1.

FIG. 3 is a diagram indicating an example of a sequence for mold closingand mold opening, in a molding process using the in-mold coatingformation apparatus shown in FIG. 1.

FIG. 4( a) is a flow chart indicating a molding process according toexample 3 which can be conducted with the use of the in-mold coatingformation apparatus shown in FIG. 1. (b) is a diagram indicating anexample of a sequence for mold closing and mold opening, for use in thesame example.

FIG. 5 is a flow chart indicating a molding process according to example4 which can be conducted with the use of the in-mold coating formationapparatus shown in FIG. 1.

FIG. 6 is a flow chart indicating a molding process according to example5 which can be conducted with the use of the in-mold coating formationapparatus shown in FIG. 1.

FIG. 7( a) is a sectional view schematically indicating a conditionwhere a mold has been closed, illustrating an in-mold coating formationmold formed according to a third aspect of the invention. (b) is anenlarged view clearly indicating an area represented by A in (a).

FIG. 8 is a view schematically indicating another example of an in-moldcoating formation mold formed according to a third aspect of the presentinvention.

FIG. 9 is a view schematically indicating a still further example of anin-mold coating formation mold formed according to the third aspect ofthe present invention.

FIG. 10 is a view schematically indicating an example of a conventionalin-mold coating formation mold which formed with an auxiliary cavity.

FIGS. 11( a) to 11(c) are explanatory views schematically indicating amolded product formed by using the in-mold coating formation moldaccording to the third aspect of the present invention. In detail, (a)is a schematic view illustrating an example of a molded product formedby using the in-mold coating formation mold shown in FIG. 7. (b) is anenlarged view partly indicating a sectional surface B of the moldedproduct. (c) is another enlarged view partly indicating a corner portionof the bottom of the molded product.

FIG. 12 is a schematic view illustrating an example of the structure ofa mold which can be suitably used in an in-mold coating formation methodaccording to a fourth aspect of the present invention.

FIGS. 13( a) to 13(d) are schematic views indicating some other examplesof the structures of molds which can be suitably used in the in-moldcoating formation method according to the fourth aspect of the presentinvention.

FIGS. 14( a) to 14(d) are schematic views showing the situation of anopening/closing operation of a mold, corresponding to various steps in amolding process using a mold structure effective for the in-mold coatingformation method according to the fourth aspect of the presentinvention, i.e., using a manner as shown in FIG. 13( a). In detail, (a)shows a mold position in which a molded resin product has just beenformed, (b) shows a mold position in which the mold has been openedafter the formation of the molded resin product, (c) shows a moldposition in which a coating material has been just injected, and (d)shows a mold position in which the mold has just been reclosed.

FIGS. 15( a) to 15(c) are used to illustrate some examples according tothe fourth aspect of the present invention, a molding process accordingto a comparative example, a molded product obtained in the moldingprocess. In detail, (a) shows a sequence for opening/closing a mold, (b)shows the shape of a molded product obtained in Comparative Example 4,and (c) shows the shape of a molded product obtained in example 7.

FIG. 16 is a flow chart indicating a molding process according toExample 8 which can be carried out with the use of the in-mold coatingformation apparatus shown in FIG. 1.

BEST MODEL FOR CARRYING OUT THE INVENTION

In the following, first to fifth aspects of the present invention willbe described in detail with reference to the accompanying drawings.However, in the following drawings, members and elements that providethe same functions will in principle be represented by the samereference numerals.

An embodiment according to the first aspect of the present inventiondirected to a method which comprises coating the surface of thethermoplastic resin molded product with a coating material so as to formcoating layer having a uniform appearance and quality by settingproperly the period for injecting the coating material and the timerequired for the completion of the reclosing step in accordance with thegel time of the coating material, at the time when the mold is opened atpredetermined interval after a thermoplastic resin material is subjectedto molding within a mold, a coating material is injected into the thusopened mold, the mold is closed again after the completion of theinjection of the coating material, the coating material is uniformlyspread within the mold under applying a pressure, and the resultant iscaused to cure.

(Time for Starting the Injection of a Coating Material)

In a method for forming a coating layer on the surface of a molded resinproduct within a mold, a time for starting the injection of a coatingmaterial may be properly selected in view of the sort of a thermoplasticresin material and a molding condition. However, the coating materialinjection should be started at the time when the surface of the moldedresin product has been cured to such an extent that it can withstand ainjection pressure and a flowing pressure of a coating material. Here,the time when the surface of the molded resin product has been cured tosuch an extent that it can withstand a injection pressure and a flowingpressure of a coating material, is meant to represent such a time atwhich the temperature of the resin is equal to or lower than its heatdistortion temperature if it is an amorphous resin, or the temperatureof the resin is equal to or lower than its crystallizing temperature ifit is a crystalline resin, with a precondition that the molded productis formed by a thermoplastic resin. Further, during a process of moldinga resin product, the surface temperature of a molded product willinherently become a function of a time. Accordingly, it is preferredthat a time period necessary for the resin to reach a temperature whichis equal to or lower than the heat distortion temperature or thecrystallizing temperature should be confirmed at each cycle for formingeach molded product, thereby facilitating a control which can determinea time for starting the injection of the coating material. For example,as shown in the following Examples 1 and 2, a coating material can beinjected at the time when the resin has been cooled for 20 seconds afterit is molded.

(Coating Material Injection Time)

In the following, description will be given mainly for explaining acoating material injection time in accordance with the first aspect ofthe present invention. However, if necessary, it is of course that sucha coating material injection time may also be used in the other aspectsof the invention. According to the first aspect of the invention, if t₁is used to represent a gel time of a coating material when it is at thetemperature of the internal surface of a mold cavity, a time necessaryfor injecting a coating material into a space formed between theinternal surface of the mold and the surface of thus obtained moldedproduct should be within a range of 0.10 t₁ to 0.99 t₁, preferablywithin a range of 0.2 t₁ to 0.8 t₁. If the coating material injectiontime is short than the above range, the pigment separation and the weldlines will become quite remarkable, thus it is not preferable. On theother hand, if the coating material injection time is longer than theabove range, during a process in which the curing reaction of thecoating material is proceeding, it is difficult for the coating materialto cover the entire molded product including its end portions, causingwrinkles and cracks to easily occur in the cured coating layer. For thisreason, a coating material injection time longer than the above range isnot preferable.

Here, “t₁” is used to represent the gel time of a coating material whenthe coating material is exposed to an internal surface temperature ofthe mold, in which the surface of the molded product is just beingcoated by the coating material. In fact, the gel time may be measuredwith the use of an ICAM-1000 Dielectro Meter (Manufactured by MicrometInstrument Inc.)

(Mold Reclosure Completion Time)

In the present specification, the mold reclosure completion time ismeant to represent a necessary time period starting from a time when thecoating material is begun to be injected into a mold, including a timeperiod for the mold to be reclosed, also including an operation timenecessary for the injected coating material to spread all over theinternal space of the mold cavity (hereinafter simply referred to asmold reclosure completion time). According to the first aspect of thepresent invention, a time period from the starting of injection of acoating material into the mold cavity until the completion of thereclosing of the mold is required to be set within a range of 0.20 t₁ to1.10 t₁ wherein t₁ is the same meaning as defined above, preferablywithin a range of 0.50 t₁ to 1.00 t₁. If a mold reclosure completiontime is shorter than the above range, a pigment contained in the coatingmaterial is likely to be separated therefrom. Moreover, if a pigmentcontained in the coating material is a flake-like material such as analuminum flake pigment, weld lines will occur remarkably. Accordingly, amold reclosure completion time shorter than the above range is notpreferable if it is desired to obtain a high quality for the outsideappearance of a molded product. On the other hand, if the mold reclosurecompletion time is longer than the above range, during a process inwhich the curing reaction of the coating material is proceeding, it isdifficult for the coating material to cover the entire molded productincluding its end portions, causing wrinkles and cracks to easily occurin the cured coating layer. For this reason, a mold reclosure completiontime longer than the above range is not preferable, either.Nevertheless, a time period starting from the completion of coatingmaterial injection until the beginning of reclosing the mold should bewithin an appropriate range of 0.00 t₁ to 0.50 t₁. Of course, accordingto other aspects of the invention, it is preferred that the moldreclosure completion time be controlled with the above range.

(Usable Synthetic Resins for the Substrate)

According to the first to fifth aspects of the present invention,molding materials capable of using in the present invention may belisted as follows. Namely, they may be thermoplastic resin materialssuch as polyethylene, polypropylene, acrylonitrile-butadiene-styrenecopolymer, polycarbonate, polyamide, polyethylene terephthalate,polybuthylene terephthalate, a modified polyphenylene ether and thelike, which can be used singly or in a mixed form, and can also be mixedinto a fiber-like filler or a flake-like filler.

(Usable Coating Materials)

Further, the coating materials capable of using according to the firstto fifth aspects of the present invention may be various known coatingmaterials suitable for use in an in-mold coating formation method. Forinstance, it is allowed to use the coating materials disclosed inJP-A-54-36369, JP-A-54-139962, JP-A-55-65511, JP-A-57-140,JP-A-60-212467, JP-A-60-221437, JP-A-1-229605, JP-A-5-70712,JP-A-5-148375, JP-A-6-107750, JP-A-8-113761.

Particularly, it is allowed to use a coating material comprising avehicle component, a pigment and polymerization initiator. Here, thevehicle component includes 20 to 70 wt % of an oligomer or its resin,such as an urethane acrylate oligomer and an epoxy acrylate oligomereach having at least two (metha)acrylate groups, or an unsaturatedpolyester resin, and 80 to 30 wt % of a copolymerizable ethylenicallyunsaturated monomer such as methyl(metha)acrylate, ethyl(metha)acrylate,propyl(metha)acrylate, butyl(metha)acrylate,2-ethylhexyl(metha)acrylate, (metha)acrylic acid, vinyl acetate,tripropylene glycol diacrylate, styrene or the like. Further, it is alsopossible to use a two-compartment type coating material such as epoxyresin/polyamine curable type one, polyol resin/polyisocyanate curabletype one, each including a main agent and a curing agent which are mixedtogether just before being injected into the mold.

The mold temperature condition suitable for carrying out the in-moldcoating formation method of the present invention, should be selectedproperly by taking into account a time for curing the surface of amolded product and a time for curing a coating material, in view of thesort of a molding material and the sort of a coating material, also inview of an actually formed molded product.

(Temperature Condition for Molding)

As related in the above, an indispensable condition for injecting acoating material is that the surface of a molded product has been curedto such an extent that it can withstand an injection pressure of acoating material, and its flowing resistance. However, if thetemperature of a mold at this time is too high, it will need a longertime necessary for the surface of the molded product to complete itssolidification, causing a problem that the molding cycle will beundesirably extended. On the other hand, if the temperature of a mold atthis time is too low, there will be another problem that the coatingmaterial curing time will become quite long, or the solidification ofthe coating material is not completed. A mold temperature providing agood balance between a curing time of the surface of a molded productand a coating material curing time should be in a temperature rangecorresponding to the specific nature of each resin molding material.However, various mold temperatures corresponding to various resinmolding materials are shown in the following Table 1 and it is preferredthat the temperature of a mold be selected from the temperature rangeslisted below. Nevertheless, it is of course that the following moldtemperature ranges may be used in any of the first to fifth aspects ofthe present invention.

TABLE 1 Temperature range Material to be used for molding for moldingPolyethylene resin  60-80° C. Polypropylene resin  80-110° C.Acrylonitrile-Butadiene-Styrene  80-100° C. copolymer resinPolycarbonate resin 110-140° C. Polyamide resin 110-140° C. Polyethyleneterephthalate resin 100-130° C. Polybutylene terephthalate resin100-130° C. Modified polyphenylene ether resin 100-130° C.

(In-Mold Coating Formation Apparatus)

FIG. 1 is an explanatory view schematically indicating an entirestructure of an in-mold coating formation apparatus (hereinafterreferred to as IMC apparatus) formed according to the present invention.It is of course that the apparatus shown in the drawing is suitable foruse in any one of the first to fifth aspects of the present invention.In detail, the IMC apparatus 100 is formed by making use of a toggletype injection molding machine, including a mold closing device 10, aninjection device 20, a control device 30 and a mold device 50.

The mold closing device 10 is comprised of a stationary platen 11 and amoving platen 12, both of which are provided for installing the molddevice 50. The moving platen 12 is guided by a tie rod 14 and can bemade to move back and forth by virtue of a hydraulic cylinder 13provided for driving the mold to close it (hereinafter, referred to asmold closing cylinder). In this way, when the moving platen 12 is movedback and forth relative to the stationary platen 11, the mold device 50can be opened or closed.

However, the toggle type injection molding machine can operate inaccordance with a relationship between the stroke amount of the moldclosing cylinder 13 and the moving amount of the moving platen 12. Thisrelationship will continuously change with the changes in the angles oftoggle links. In the area just before the toggle links become straightlines, the moving amount of the moving platen 12 will become small withrespect to the stroke amount of the mold closing cylinder 13, while atthe same time the mold closing cylinder 13 is driven continuously byvirtue of a relatively low oil pressure, thereby producing a large moldclosing force.

Therefore, if compared with a direct press type injection mold machinecapable of directly driving a mold by virtue of a hydraulic cylinder,the toggle type injection molding machine is characterized in that itcan provide a desired driving action by virtue of the mold closingcylinder 13 having an excellent driving property and particularly anexcellent high speed driving property, and that it can control theposition of the mold device 50 with an extremely high efficiency byvirtue of a force doubling mechanism of the mold closing device 10.Further, the toggle type injection molding machine is characterized inthat it can produce a sufficiently strong mold closing force. Inaddition, with the use of its excellent driving property, as will bedescribed later in the present specification, the IMC method (in-moldcoating formation method) may be used so that a coating material may beinjected into the mold cavity, the injected coating material is thencaused to spread uniformly all over the internal surface of the moldcavity, thereby making it possible for the coating material to be cureduniformly, thus obtaining a desired coating layer formed on the surfaceof a molded product.

The injection device 20 comprises a screw member 21 having a spiral flatportion and a barrel 22 enclosing the screw 21, in a manner such thatthe screw member 21 may be driven by a hydraulic motor 23 so as to movefreely back and forth along the internal surface of the barrel 22. Inthis way, with the rotation of the screw member 21, an amount of resinpellets supplied to a hopper 25 will be sent toward the screw member 21.Meanwhile, the resin pellets are heated by virtue of a heater (notshown) attached on the outer surface of the barrel 22, so that the resinpellets may be melted within the barrel through a kneading action byvirtue of the rotation of the screw member 21.

Once an amount of a molten resin being sent forward along the screwmember 21 arrives at a predetermined value, the driving operation of thehydraulic motor 23 is stopped, and at the same time an injectioncylinder 24 is driven so that the screw member 21 is caused to moveforwardly. As a result, the molten resin material accumulated in thefront area of the screw member 21 will be injected through a nozzle 26into a mold cavity 53 of the mold device 50.

The mold device 50 comprises a fixed mold portion 51 attached on thestationary platen 11 and a movable mold portion 52 attached on themoving platen 12. The movable mold portion 52 includes a coatingmaterial injection device 55 for injecting a coating material into themold cavity 53, and a coating material pressure sensor 54 for detectingthe coating material injected in the mold cavity 53. However, for use asthe mold device 50, it is preferred to use a mold according to thesecond aspect of the invention or a mold according to the third aspectof the invention.

Next, the structure of the control device 30 will be described. As shownin FIG. 1, the control device 30 has a molding device control section 31and an injection control section 38. The molding device control section31 can effect an interlocking between the mold closing device 10 and theinjection device 20 and can totally control an entire system of thecontrol section 30. The injection control section 38 can control theoperation of the injection device 20. The two control sections 31 and 38have controlling functions similar to a control section of a commoninjection molding machine.

On the other hand, a control section having the control functioninherent in the IMC apparatus 100 of the present invention has aninjection machine control section 35 and a changing pattern storingsection 34. The injection machine control section 35 is provided toreceive a molding condition data signal (which means a changing patternof a molding condition and will have the same meaning in the following)from a mold closing condition setting section 32 so as to control theoperation of the mold closing device 10. The changing pattern storingsection 34 is provided to receive from the mold closing conditionsetting section 32 some molding condition data signals such as a moldopening amount of the mold portions 51, 52 (hereinafter referred to as“mold opening amount”) and a mold closing force of the mold portions 51,52 (hereinafter referred to as “mold closing force”), and to convertthese data signals into the molding condition data signals of the strokeof the mold closing cylinder 13 and to send these signals to the moldclosing control section 33.

Here, the mold closing condition setting section 32 is provided to setvarious molding conditions such as an opening/closing speed of the moldclosing device 10, its operation timing, its mold opening amount, itsmold closing force, and an injecting amount of the coating materialinjection device 55, its injection speed, its injection timing, itsinjection pressure, and a pressure of the coating material within themold cavity 53. In this way, the molding condition data signals relatingto an injecting amount of the coating material injection device 55, itsinjection speed, its injection timing and its injection pressure aresent from the mold closing condition setting section 32 to an injectionmachine control section 35. On the other hand, the molding conditiondata signals relating to an opening/closing speed of the mold closingdevice 10, its operation timing and a pressure of the coating materialwithin the mold cavity 53 are sent from the same mold closing conditionsetting section to a mold closing control section 33. Further, as to themolding conditions relating to a mold opening amount and a mold closingforce, their molding condition data signals are sent to the abovechanging pattern storing section 34.

Nevertheless, the changing pattern storing section 34 is required tostore in advance two kinds of correlations before it is put into itscontrolling operation. One correlation is a relationship between a moldopening amount and a stroke of the mold closing cylinder 13, while theother correlation is a relationship between a mold closing force and astroke of the mold closing cylinder 13.

For this reason, after the mold device 50 has been attached on to thestationary platen 11 and the moving platen 12, it is necessary to usethe same procedure as in a common injection molding machine to perform acorrelation calculation under a condition where a die height adjustmentand a mold closing force adjustment have been completed in accordancewith mold thickness (die height) of the mold device 50. In detail, thecorrelation calculation is performed under a condition where the molddevice 50 is being opened and closed for the purpose of adjustment andthe calculation itself is conducted in the changing pattern storingsection 34 which can continuously receive several detection signals fedfrom a stroke sensor 16, a mold opening amount sensor 17, a mold closingforce sensor 18, thereby obtaining and storing a correlation between amold opening amount and a stroke of the mold closing cylinder 13, andanother correlation between a mold closing force and a stroke of themold closing cylinder 13.

In the following, some detailed examples will be given to explain anoperation of the IMC apparatus 100 for carrying out the IMC method whichuses the IMC apparatus 100 having the control device 30 constructed inthe above described manner.

At first, a feedback control is conducted by virtue of a control signalfed from the mold closing control section 33 and also by virtue of amold closing servo valve 15, while at the same time the movable moldportion 52, driven by the mold closing cylinder 13 and in accordancewith a mold closing speed pattern set in the mold closing conditionsetting section 32, is moved forward from its opening limit position sothat movable mold portion 52 can get in contact with the fixed moldportion 51. After that, the feedback control is performed by virtue of acontrol signal fed from the mold closing control section 33 and a moldclosing servo valve 15, while at the same time the movable mold portion52, driven by the mold closing cylinder 13 and in accordance with amolding condition data signal of a mold closing force (a changingpattern of a mold closing force) set in the mold closing conditionsetting section 32, is moved forward still further. In this way, a tierod 14 is extended so that a predetermined mold closing force is exertedon the mold device 50.

A molten resin stored in the front portion of the screw 21 is injectedthrough a nozzle 26 into the mold cavity 53 when the screw 21 is causedto proceed forwardly by the injection cylinder 24, while controlling anopening degree of an injection servo valve 27 according to the controlsignal fed from the injection control section 38 in predetermined timingduring the operation of the mold closing device 10 mentioned above,thereby forming a thermoplastic resin molded product. On the other hand,in order to achieve an interlock effect between the operation of theclosing device 10 and the operation of the injection device, theoperation timing signals of the two devices can be transmitted betweenthese two devices by the molding control section 31.

Subsequently, the movable mold portion 52 is caused to move back byvirtue of the mold closing cylinder 13. Then, a feedback control isconducted by virtue of a control signal fed from the mold closingcontrol section 33 and also by virtue of a mold closing servo valve 15,while at the same time providing a predetermined mold opening amount setin the mold closing condition setting section 32, thereby forming a gapbetween the surface of the thermoplastic resin molded product and theinternal surface of the mold cavity. After that, in accordance with aninjecting amount of the coating material injection device 55, itsinjection speed, its injection timing, its injection pressure which areall set in the mold closing condition setting section 32, the coatingmaterial injection device 55 will be driven by a control signal fed fromthe injection machine control section 35, so as to inject the coatingmaterial into the mold cavity 53.

Afterwards, a feedback control is conducted by virtue of a controlsignal fed from the mold closing control section 33 and also by virtueof a mold closing servo valve 15, while at the same time the movablemold portion 52 is again caused to move forward by virtue of the moldclosing cylinder 13, thereby effecting an operation in accordance with adata signal of a mold reclosing condition (a mold opening amountchanging pattern) and an operation in accordance with a data signal of amolding condition of a coating material (a pressure pattern of thecoating material), which data signals are all set in advance in the moldclosing condition setting section 32. In this way, the injected coatingmaterial is caused to spread over the entire surface of thethermoplastic resin molded product, thereby providing an optimum moldingcondition for the appearance and the adhesion strength of the coatinglayer.

On other hand, in order for the coating layer to stabilize its outsideappearance and its adhesion strength, it is preferred to use the coatingmaterial pressure sensor 54 to perform a feedback control in accordancewith a predetermined coating material pressure pattern. In particular,as shown in Example 3 which will be described later in the presentspecification, if an internal pressure within a mold containing aninjected coating material is at first increased immediately after theinjection of the coating material, and then is gradually reduced to makethe internal pressure to change gradually step by step, the injectedcoating material will be allowed to spread more uniformly within themold, making it possible to use a coating material having a highviscosity.

However, if it is difficult to dispose the coating material pressuresensor 54 in the mold device 50, a mold closing force pattern may be setto replace the above coating material pressure pattern, therebyeffecting a feed back control in accordance with the mold closing forcepattern.

Subsequently, a feedback control is conducted again by virtue of acontrol signal fed from the mold closing control section 33 and also byvirtue of a mold closing servo valve 15, while at the same time themovable mold portion 52 is caused to operate in accordance with anoperation timing and a mold opening speed pattern set in advance in themold closing condition setting section 32, so that the movable mold ismoved back to its opening limit position, and an integrally formedmolded product is taken out from the mold device 50. In this way, onecycle of molding process is thus completed.

As described in the above, with the use of the present invention, themold closing speed pattern, the mold closing force pattern, the moldopening amount pattern and the mold opening speed pattern, all set inadvance in the mold closing condition setting section 32, can all beunified into a stroke pattern of the mold closing cylinder so as to besubjected to the feedback control. Consequently, even under a moldingcondition where the mold closing force and the mold opening amount arealternatively repeated, a control object will still be the strokepattern of the mold closing cylinder.

For this reason, since it is allowed to ensure a continuous controlwithout involving the change of the control object, it is possible toobtain a high response capable of dealing with a rapidly changingpattern. Namely, since the above described simplified control system canbe used in the toggle type injection molding machine which inherentlyhas a high response and a high precision, these desired characteristicsare allowed to exhibit to their maximum extents. In this way, a processbeginning with the injection of a coating material into the mold andending with the solidification of the coating material, will be kept ata high response, and may be driven and controlled with a high precision,thereby making it sure to stabilize the state of a formed coating layer,increase the yield of the molded products, shorten the manufacturingcycle and improve the productivity.

Next, detailed description will be made to explain an embodimentaccording to the second aspect of the present invention. However, thepresent invention is by no means to be limited to such an embodiment.

Similar to the manner described in the above, in this embodiment of thepresent invention, the mold closing speed pattern, the mold closingforce pattern, the mold opening amount pattern and the mold openingspeed pattern, all set in advance in the mold closing condition settingsection 32 of the in-mold coating formation apparatus shown in FIG. 1,can all be unified into a stroke pattern of the mold closing cylinder soas to be subjected to a feedback control. Consequently, even under amolding condition where the mold closing force and the mold openingamount are alternatively repeated, a control object will still be thestroke pattern of the mold closing cylinder.

For this reason, since it is allowed to ensure a continuous controlwithout involving the change of the control object, it is possible toobtain a high response capable of dealing with a rapidly changingpattern. Namely, since the above described simplified control system canbe used in the toggle type injection molding machine which inherentlyhas a high response and a high precision, these desired characteristicsare allowed to exhibit to their maximum extents. In this way, a processbeginning with the injection of a coating material into the mold andending with curing time of the coating material, will be kept at a highresponse, and may be driven and controlled with a high precision,thereby making it sure to stabilize the state of a formed coating layer,increase the yield of the molded products, shorten the manufacturingcycle and improve the productivity.

Nevertheless, when using the IMC methods and the IMC apparatus of thepresent invention, the mold portions 51, 52 are preferred to be shearedge type ones. Of course, it is also possible to use flat parting typemolds if they are required to be so used in view of the shape of anobject product.

However, although a thermoplastic resin injection molding process oftenuses flat parting type molds, at this time a part of a mold closingforce generated in an injection molding machine will be converted into acompressive force compressing the thermoplastic resin molded product andthe coating material. In fact, such a part of the mold closing force isreceived on the parting surfaces of the mold. Further, the mold closingforce will change with the lapse of time, depending upon a volume changecaused due to a temperature change of the molded resin product and thecoating material in the mold and also due to a curing shrinkage of thesematerials. For this reason, when using a flat parting type mold, merelythe control of the mold closing force is not sufficient for controllingthe compressing force which compresses the thermoplastic resin moldedproduct and the coating material.

On the other hand, if a coating material pressure sensor is attached ina mold and if the feedback control is performed in accordance with apredetermined coating material pressure pattern, even under a conditionwhere the state of a coating layer within the mold will be differentfrom one coating material injection to another, it is still possible toeffect a desired control of a molding condition, so that it is sure fora formed coating layer to obtain a stabilized outside appearance and astabilized adhesion strength.

On the other hand, in a prior art a shear edge type mold is often usedto deal with SMC and BMC resins. In such a case, almost all the moldclosing forces produced in an injection molding machine will beconverted into a compressive force (coating material pressure) whichcompresses the thermoplastic resin molded product. As a result, it ispossible to form a desired coating layer having predeterminedcharacteristics, only through a feedback control of the mold closingforce.

Although it has been described in the above that the IMC apparatus 100can be a toggle type injection molding machine, it is also possible touse a toggle type electric injection molding machine in place of theabove mentioned toggle type injection molding machine. In this case, itis allowed to use a mold closing ball screw in place of the mold closingcylinder, and to use a mold closing servo motor in place of the moldclosing servo valve. Accordingly, the IMC method and IMC apparatus ofthe present invention should not be limited to the above specificallydescribed method and apparatus. In fact, it is also possible to performsome different but appropriate operations in accordance with somespecific requirements demanded by an actual molding process. However,some different operations of the inventive method will be described inthe following examples of the present invention.

Next, description will be given and the accompanying drawings will bereferred to explain in detail an in-mold coating formation mold and anin-mold coating formation method (IMC), according to an example of thethird aspect of the present invention. However, the present invention isby no means to be limited to the following specific example.

FIG. 7( a) (a figure on the left side) is a sectional view schematicallyindicating one embodiment of an in-mold coating formation mold(hereinafter, referred to as IMC mold) which can be used in the thirdaspect of the present invention. In fact, the figure is used to show acondition where the mold has just been closed. In detail, the IMC mold50 comprises a fixed mold portion 51 and a movable mold portion 52,which are engaged with each other through a shear edge portion 3 to forma mold cavity 4. The fixed mold portion 51 is provided with a hot runner15 which is used to inject a molten resin. On the other hand, themovable mold 52 is provided with a coating material injection device 55which is used to inject a coating material into the mold cavity 4 inorder that a coating layer can be formed on the surface of athermoplastic resin product molded in the IMC mold 50. In fact, thecoating layer formation is completed within the IMC mold 50. Although itis not shown in FIG. 7( a) that there is a moving device for moving themovable mold portion 52, the movable mold portion 52 is in fact openedand closed in a direction shown by an arrow M in FIG. 7.

FIG. 7( b) (a figure on the right side) is an enlarged view showing indetail an area in the vicinity of the shear edge portion 3, with saidarea being represented by a reference A in FIG. 7( a). As shown in thefigure, an auxiliary cavity 7 is formed and it is extending in theopening/closing direction of the movable mold portion 52. Further, theshear edge portion 3 of the fixed mold portion 51 has been processedinto such a configuration that the entire internal surface of the moldcavity 4 is communicated with the shear edge portion. In this manner,the molten resin introduced into the auxiliary cavity 7 will be formedinto an “auxiliary molded body” integrally formed with the moldedproduct formed within the mold cavity 4.

However, the auxiliary cavity 7 can be formed in a manner shown in amold 150 illustrated in FIG. 9 which schematically indicates a mold usedin an example according to the third aspect of the present invention.Namely, the auxiliary cavity is allowed to be formed by taking intoaccount the shape of a molded resin product, the position of a spruesection and the position of a coating material injecting device, and byprocessing the shear edge portion of the movable mold. In other words,it is not necessary to pay attention as to which mold portion should bedesignated as a fixed mold portion and which mold portion should bedesignated as a movable mold portion. Instead, what is necessary to bedone is only that when the mold is divided into a male mold and a femalemold, the shear edge portion of the male mold is processed to form theauxiliary cavity so as to form an auxiliary molded body. However, if themold has not been divided into a male mold and a female mold, what isnecessary to be done is only to form an auxiliary cavity in a mold whosesurface is opposite to the coating layer of the molded product.

Referring to FIG. 7( a), when a coating material has been injected fromthe coating material injecting device 55, the injected coating materialwill spread through an internal space formed between the inner surfaceof the movable mold 52 and a molded main body, so as to arrive at theshear edge portion 3. At this time, some gaps possible for the coatingmaterial to leak outwardly through the shear edge portion 3 is allowedto form, by virtue of a shrinkage in a thickness direction (a verticaldirection in FIG. 7( a)), in the molded main body formed within the moldcavity 4 and in the auxiliary body formed within the auxiliary cavity 7.In addition, when an injection pressure of the coating material is high,the cured resin will be compressed so as to shrink, thus forming theabove mentioned gaps. In any case, a shrinkage of a resin material isproportional in its extent to a thickness of a molded body.

Therefore, in the case where the auxiliary cavity 7 has not been formed,since a molded body will shrink greatly in its thickness direction, acoating material will flow to enlarge the gap formed between the moldedbody and the inner surface of the movable mold portion 52, hence flowingeasily into the shear edge portion 3 and then out of the mold. This isbecause the shear edge portion 3 has a gap which, under a certainpredetermined pressure, will not allow a resin to be used for moldingusually having a high viscosity to flow thereto, but will allow thecoating material which usually has a low viscosity to flow thereto.

On the other hand, in the case where the auxiliary cavity 7 has beenformed and an auxiliary molded body having a small thickness is existingin the cavity, since an absolute value of a shrinking amount in thethickness direction of the auxiliary molded body is small, a gap formedin the above described manner will not be large enough to cause thecoating material to leak out of the mold, thereby preventing the leakageof a coating material. Further, as may be clearly understood from theopening/closing direction of the movable mold portion 52, the gap formeddue to a shrinkage in the molded main body and the auxiliary molded bodywill not change in its size even under a condition where the movablemold portion 52 has been opened to some extent in order to inject acoating material. Therefore, with the use of the IMC mold 50 formedaccording to the third aspect of the present invention, we can easilycarry out the injection of a coating material and its solidificationeven when the movable mold portion 52 has been opened to some extent.

Preferably, the thickness D of the auxiliary cavity 7 is set to bewithin a range of 0.1 mm to 2 mm, while its length L (extending in theopening/closing direction of the movable mold portion 52) is set to bewithin a range of 0.5 mm to 30 mm. If the thickness D is too small, itwill be difficult to fill the narrow space with a resin and hence it isdifficult to form an auxiliary molded body. On the other hand, if thethickness is too large, a gap caused due to the above describedshrinkage will be enlarged, thus losing a desired effect of preventingthe leakage of a coating material. Now, if the length L is too short, itis difficult to ensure a sufficient effect of preventing the leakage ofa coating material. On the other hand, if the length is too long, itwill be difficult to completely fill the long space with a resin andwill thus cause a waste of the resin.

However, the IMC mold 50 should not be limited to the above describedshear edge type. In fact, it is also allowed to use another IMC mold 50shown in FIG. 8, which comprises a fixed mold portion 51 and a movablemold portion 52, having parting surfaces 123. In detail, one end of anauxiliary cavity 7 is connected with the parting surfaces 123. Such anIMC mold 50 having such a parting structure may be used as a mold in thethird aspect of the present invention. FIG. 8 is a view schematicallyshowing a condition where the mold has just been closed. As shown in thefigure, the resin injected into the auxiliary cavity 7 having a smallthickness has only a small shrinking amount in its thickness direction,so that the coating material can be prevented from flowing out to theparting surfaces 123, thereby ensuring a desired solidification of thecoating material within the auxiliary cavity 7.

In addition, with regard to the IMC mold 50, in order to enhance thesolidification of the coating material in the auxiliary cavity 7 and toexactly prevent the coating material from flowing out of the mold, it ispreferred to perform a treatment shown in FIG. 7( b). Namely, in orderto keep at a high temperature an internal surface on the coatingmaterial injection side of the auxiliary cavity 7, i.e., a part of theauxiliary cavity's internal surface which is located close to themovable mold portion 52 and receives an injection of the coatingmaterial, it is preferred to provide a heater 131 so as to form aheating block 132. At this time, when a thermosetting coating materialis caused to flow through a gap formed between the heating block 132 andthe auxiliary molded body formed in the auxiliary cavity 7, theviscosity of the thermosetting coating material will become high, sothat the curing reaction of the coating material is enhanced, therebyexactly preventing it from flowing out of the mold. In FIG. 8, althoughthe heater is not shown, such a heater may be proved within the heatingblock in the same manner as shown in FIG. 7( b). In addition, withregard to any type of a mold, a heating block is not necessary to beseparated from the mold. Instead, it is always possible that the heatingblock 131 may be directly buried in the mold.

With the use of the IMC mold 50 formed according to the third aspect ofthe present invention, since an auxiliary molded body is formed which ishowever not necessary in forming a common thermoplastic resin product,an additional step becomes necessary to remove the auxiliary molded bodyafter the molding process. In this way, although it is necessary tocarry out an additional step to remove the auxiliary molded body, usingthe mold formed according to the third aspect of the present inventioncan provide at least the following advantageous as compared with thecase where there is existing the coating material leakage. Namely, if acoating material is leaked during an injection molding process, all themolds within the injection molding machine have to be cleaned. As aresult, a growing cycle for forming a molded resin product will becomeundesirably long, resulting in a low productivity. Moreover, since themolded product growing cycle becomes irregular, it is difficult toensure a constant quality for the molded resin products, resulting inlow product quality. Therefore, with the use of the IMC mold 50 formedaccording to the third aspect of the present invention, it is sure toobtain some remarkable effects including an increased productivity and amore stabilized product quality.

In the following, description will be made to explain about anappropriate condition suitable for carrying out the in-mold coatingformation method (IMC) using the IMC mold formed according to the thirdaspect of the present invention.

In view of the purpose of preventing a coating material leakage,according to the IMC method of the third aspect of the presentinvention, the temperature of a surface portion on the coating materialinjection side of the auxiliary cavity is made higher than otherportions, so that the coating material spread from the mold cavity canbe cured within the auxiliary cavity. One method of forming atemperature distribution within the mold is to perform a temperaturecontrol in the same manner as shown in FIG. 7 and FIG. 8. Namely, aheater is buried in the vicinity of a surface portion on the coatingmaterial injection side of the auxiliary cavity, thereby forming aheating block and thus facilitating the desired temperature control. Inpractice, the temperature of the mold at this time may be controlled atan appropriate value by taking into account a curing condition(temperature and time) of a coating material and the thermal plasticityof the resin to be used for molding.

Further, in order to prevent a coating material from flowing out of amold, it is necessary that the auxiliary cavity be completely filledwith a resin to be used for molding. However, in order to completelyfill the auxiliary cavity with the resin to be used for molding, it ispreferred that a molten resin receives a higher pressure which is higherthan a pressure necessary for filling the mold cavity with the resin tobe used for molding. Namely, it is preferred that a mold closing forcebe controlled in a manner such that a high mold closing force may beobtained which is higher than a mold closing force for use in a moldingformation process using a mold not having an auxiliary cavity, so thatthe auxiliary cavity may be filled with the resin to be used formolding, using an injection filling pressure which is higher than ausual injection filling pressure.

Of course, it is also preferred to use the in-mold coating formationapparatus according to the second aspect of the present invention, forcarrying out the IMC method described in the third aspect of the presentinvention.

However, as to the IMC method according to the third aspect of thepresent invention, although the method may be used to manufacture manykinds of products without any limitation, preferably it is used toproduce the following product items including a bumper, a door mirrorcover, a fender, a door panel, a back door panel, an over fender, a doorhandle, a side garnish, a side protector, a wheel cap, all for use in anautomobile vehicle, and also including a side cover and a cowl for usein a motorcycle.

Next, description will be given to explain an example of an in-moldcoating formation method (IMC) according to a fourth aspect of thepresent invention, with reference to the accompanying drawings. However,the fourth aspect of the present invention is by no means to be limitedto the following specific example.

At first, description will be made to explain one embodiment of the IMCmethod using the IMC apparatus 100 having the control device 30constructed in the above described manner. Further, the description willalso include an operation of the IMC apparatus 100.

At first, a feedback control is conducted by virtue of a control signalfed from the mold closing control section 33 and also by virtue of amold closing servo valve 15, while at the same time the movable moldportion 52 is moved by the mold closing cylinder 13 so that the movablemold portion 52 moves forwardly from its opening limit position inaccordance with a mold closing speed pattern (a data signal representinga mold closure operating pattern) set in advance in the mold closingcondition setting section 32. Thus, the movable mold portion 52 gets incontact with the fixed mold portion 51. Afterwards, another feedbackcontrol is conducted by virtue of a control signal fed from the moldclosing control section 33 and also by virtue of a mold closing servovalve 15, while at the same time the movable mold portion 52 is moved bythe mold closing cylinder 13 so that the movable mold portion 52 movesforward still further, in accordance with a mold closing pattern set inadvance in the mold closing condition setting section 32. In this way,the tie rod 14 is extended, applying a predetermined mold closing forceto the mold device 50.

In this way, according to an operation timing predetermined foroperating the mold closing device 10, the opening amount of theinjection servo valve 27 is controlled in accordance with a controlsignal fed from the injection control section 38, while at the same timethe screw member 21 is moved forward by virtue of an injection cylinder24. As fast as this is done, the molten resin accumulated around thefront portion of the screw 21 is injected into the mold cavity 53 by wayof the nozzle 26, thereby forming a thermoplastic resin molded product.However, in order to form an interlock between the operation of the moldclosing device 10 and the operation of the injection device 20, the molddevice control section 31 is so formed that the operation timing signalsof the two devices may be transmitted therethrough.

Next, the movable mold portion 52 is moved by the mold closing cylinder13 so that the movable mold portion 52 moves backwardly. Meanwhile, afeedback control is conducted by virtue of a control signal fed from themold closing control section 33 and also by virtue of a mold closingservo valve 15, while at the same time the mold is opened by apredetermined opening amount set in advance in the mold closingcondition setting section 32, thereby forming a gap between the surfaceof the thermoplastic resin molded product and the internal surface ofthe mold cavity 53. Then, in accordance with an injection amount of thecoating material injection device 55, an injection speed of the coatingmaterial, an injection timing and an injection pressure, all set inadvance in the mold closing condition setting section 32, the coatingmaterial injecting device 55 is driven so that the coating material isinjected into the mold cavity 53, by virtue of a control signal fed froman injection apparatus control section 35.

Next, a feedback control is conducted by virtue of a control signal fedfrom the mold closing control section 33 and also by virtue of a moldclosing servo valve 15, while at the same time the movable mold portion52 is moved by the mold closing cylinder 13 so that the movable moldportion 52 moves forwardly still further, thereby carrying out a moldopening amount pattern and an in-mold coating material pressure patternwhich are all set in advance in the mold closing condition settingsection 32. However, in carrying out the in-mold coating materialpressure pattern, it is needed to feed back a detected value of thecoating material pressure sensor 54.

In this way, an injected coating material is caused to spread over theentire surface of a thermoplastic resin molded product, with attainingat the same time an optimum molding condition for the appearance and theadhesion strength of the coating layer. However, in the case where amold not having a coating material pressure sensor 54 is used, a moldclosing pattern can be set and executed in place of the above in-moldcoating material pressure pattern.

After that, a feedback control is conducted by virtue of a controlsignal fed from the mold closing control section 33 and also by virtueof a mold closing servo valve 15, while at the same time the movablemold portion 52 is moved by the mold closing cylinder 13 so that themovable mold portion 52 moves backwardly to arrive at its opening limitposition, in accordance with an operation timing and a mold openingspeed pattern set in advance in the mold closing condition settingsection 32. Then, an integrally formed molded product may be taken outof the mold device 50, thereby completing the cycle of molding one resinproduct.

In carrying out the above described IMC method, according to the presentinvention, the structure of a mold, a molding formation method and amolding formation condition may be made sufficiently appropriate so thatthe coating material injected in the mold cavity 53 can be preventedfrom leaking out of the mold. FIG. 12 is an explanatory viewschematically indicating one example of a sealing method for effecting asealing between the mold structure and the coating material.

As shown in FIG. 12, the mold portions 51 and 52 are preferred to beflat parting type mold portions which together form a sub-cavity. Here,the parting surface of the movable mold portion 52 is formed with asub-cavity 58 which is communicated with the mold cavity 53. Further,the movable mold portion 52 is formed with a groove 59 which iscommunicated with the sub-cavity 58. Here, the sub-cavity 58 and thegroove 59 are not necessarily to be limited to any particular shapes.Instead, they can be formed into various shapes shown in FIGS. 13( a) to13(d). On the other hand, in order to reduce the production cost formanufacturing the molds, it is preferred that the molds be made simplein their shapes and easy to be processed. However, the sub-cavity 58 andthe groove 59 are preferred to be made as small as possible, providedthat they are effective in receiving extra amount of a coating materialflowing into the parting surfaces of the mold portions 51 and 52.

At first, the mold portions 51 and 52 are used to form a thermoplasticresin molded product. In order to prevent the resin to be used formolding from flowing into the parting surfaces of the mold portions 51and 52, the parting surfaces of the mold portions 51 and 52 are requiredto be in a completely contacted position so that an interface thusformed may be completely sealed. Alternatively, an interval between thetwo parting surfaces is controlled at a predetermined width so that itis possible to make use of the viscosity of the resin to be used formolding under a predetermined molding pressure, so as to prevent themolding resin from flowing into the parting surfaces.

Then, the mold portions 51 and 52 are opened so as to form apredetermined interval therebetween, so that a predetermined amount of acoating material may be injected through the coating material injectingdevice 55 into the mold cavity 53. As soon as the coating materialinjection is finished, the mold portions 51 and 52 are closed. At thistime, an in-mold coating material pressure should be controlled in amanner such that it becomes 5 MPa to 15 MPa at least in an area wherethe thermoplastic resin molded product receives the lowest pressurewithin the mold.

FIGS. 14( a) to 14(d) are used to explain a process including molding ofa resin, coating material injection and closing of the mold. In detail,these figures are used to illustrate a condition indicating how a resinproduct may be molded and how a coating layer can be formed by using thesub-cavity 58 and the groove 59 having the shapes shown in FIG. 13( a).Here, although a resin to be used for molding 81 is caused to fulfillthe mold cavity 53 and the sub-cavity 58 and the groove 59, the resinwill not flow outwardly to the parting faces of the mold portions 51 and52.

In this way, the mold portions 51 and 52 are opened so as to form apredetermined interval therebetween, an amount of coating material 82 isthen injected between the two mold portions. Subsequently, even thoughthe mold is closed so that the coating material 82 is caused touniformly spread over the entire surface of the molded resin product 81,an extra amount of the coating material 82 will be received into thegroove 59. In this manner, even if the molded resin product 81 is causedto deform to some extent, the coating material can be exactly preventedfrom flowing out to the parting surfaces of the thus formed mold.

In this way, after a high pressure of 5 MPa to 15 MPa has been applied,an in-mold coating material pressure can be controlled in a manner suchthat it becomes 0.5 MPa to 2 MPa at least in an area where thethermoplastic resin molded product receives the lowest pressure withinthe mold. Here, “an area where the thermoplastic resin molded productreceives the lowest pressure in the mold” means an in-mold zone whichreceives the lowest pressure in the mold. In practice, such an in-moldzone is often used to mean the front portion of an auxiliary cavitywhich is located the farthest from the resin injection section. In thisway, by at first applying a high pressure, it is possible for thecoating material to flow over the entire surface of the thermoplasticresin molded product, so that coating material can completely cover andtightly adhere to the surface of the molded product, thereby making itsure to have a uniform adhesion strength irrespective of positions ofthe thermoplastic resin molded product. Further, by setting pressure ata relatively low level when the coating material is caused to cure, itis possible to obtain an effect obtainable in an example according tothe fourth aspect of the invention which will be discussed later.Namely, it is possible to prevent the occurrence of some humps(actually, tubercles which will possibly be formed on the surfaces ofsome thick portions of a molded product), thereby making it possible toobtain an integrally formed molded resin product having a coating layerformed in a good state.

The basic concept of the in-mold coating formation method (IMC)according to the fifth aspect of the present invention is to effectivelymake use of a heat held within a molded resin in a mold, so that thisheat can be effectively used to cure a thermosetting coating material.In this way, the temperature of the mold is allowed to be set lower thanthe curing temperature of the coating material so as to improve theproductivity. Further, it is also possible to cure a coating materialunder a predetermined condition so as to obtain a coating layer havinggood physical properties.

In the following, description will be given to explain in detail anexample according to a fifth aspect of the present invention, withreference to the accompanying drawings. However, it should be understoodthat the fifth aspect of the present invention is by no means to belimited to the following example.

In the following example, it is also preferred to use the in-moldcoating formation apparatus (hereinafter, referred to as IMC apparatus)100 formed by using a common toggle type injection molding machine shownin FIG. 1.

Next, description will be given to explain the operation of the IMCapparatus 100 for carrying out the IMC method of the present invention.In fact, the IMC method is carried out by using the IMC apparatus 100having the control device constructed in the above described manner.However, since a temperature sensor is used as a control element 54 inthis example, the following description will be given to mainly explaina control method involving the use of the temperature sensor.

At first, a feedback control is conducted by virtue of a control signalfed from the mold closing control section 33 and also by virtue of amold closing servo valve 15, while at the same time the movable moldportion 52 is moved by the mold closing cylinder 13 so that the movablemold portion 52 moves forwardly from its opening limit position to getin contact with the fixed mold portion 51, in accordance with a datasignal representing a mold closing speed (mold closing speed pattern)set in advance in the mold closing condition setting section 32. Soonafterwards, another feedback control is conducted by virtue of a controlsignal fed from the mold closing control section 33 and also by virtueof a mold closing servo valve 15, while at the same time the movablemold portion 52 is moved by the mold closing cylinder 13 so that themovable mold portion 52 moves forwardly still further, in accordancewith a data signal representing a mold closing force formation condition(mold closing force pattern) set in advance in the mold closingcondition setting section 32. In this way, the tie rod 14 is extended sothat a predetermined mold closing force is applied to the mold device50.

A molten resin stored in the front portion of the screw 21 is injectedthrough a nozzle 26 into the mold cavity 53 when the screw 21 is causedto proceed forwardly by the injection cylinder 24, while controlling anopening degree of an injection servo valve 27 according to the controlsignal fed from the injection control section 38 in predetermined timingduring the operation of the mold closing device 10 mentioned above,thereby a thermoplastic resin molded product is formed. However, inorder to form an interlock between the operation of the mold closingdevice 10 and the operation of the injection device 20, the mold devicecontrol section 31 is so formed that the operation timing signals of twodevices may be transmitted therethrough.

Next, at the time when it is judged that the surface portion of athermoplastic resin molded product has been cured by virtue of a surfacetemperature of the molded resin product, a feedback control is conductedby virtue of a control signal fed from the mold closing control section33 and also by virtue of a mold closing servo valve 15, while at thesame time the mold portions 51 and 52 are opened so as to form apredetermined interval therebetween. However, an opening amount of themold portions 51 and 52 is preferred to be within a range of 0.5 mm to 2mm. In this way, it becomes possible to inhibit the heat diffusion fromthe surface of the molded resin product to one of the mold portions.Thus, a heat held in the thermoplastic resin molded product will causethe surface temperature of the molded product to rise to a value whichis equal to or higher than the curing temperature of the coatingmaterial. Subsequently, in accordance with a coating material injectingamount of the coating material injection device 55, its injection speedand its injection pressure, all set in advance in the mold closingcondition setting section 32, the coating material injection device 55is driven by virtue of a control signal fed from the injection controlsection 35, so that the coating material is injected into the moldcavity 53.

Afterwards, another feedback control is conducted by virtue of a controlsignal fed from the mold closing control section 33 and also by virtueof a mold closing servo valve 15, while at the same time the movablemold portion 52 is moved by the mold closing cylinder 13 so that themovable mold portion 52 moves forwardly still further, executing a datasignal representing a mold opening amount formation condition (moldopening amount changing pattern) and a mold closing force pattern, allset in advance in the mold closing condition setting section 32. In thisway, the injected coating material is allowed to spread over the entiresurface of the thermoplastic resin molded product, thereby ensuring themost appropriate condition for forming a coating layer having anexcellent outside appearance and a high adhesion strength.

Subsequently, a feedback control is conducted by virtue of a controlsignal fed from the mold closing control section 33 and also by virtueof a mold closing servo valve 15, while at the same time the movablemold portion 52 is moved by the mold closing cylinder 13 so that themovable mold portion 52 moves backwardly to arrive at its opening limitposition, in accordance with an operation timing and a mold openingspeed pattern set in advance in the mold closing condition settingsection 32. Then, an integrally formed molded product may be taken outof the mold device 50, thereby completing the cycle of molding one resinproduct.

The above description has explained only the basic operation of the IMCapparatus 100. According to the IMC method of the present invention, theinjection of the coating material during one cycle of molding is carriedout under a condition where the surface temperature of a thermoplasticresin molded product is higher than the curing temperature of thecoating material, but with the mold temperature in the mold cavity beinglower than the coating material curing temperature. However, atemperature difference between the mold temperature within the moldcavity and the coating material curing temperature is preferred to beset at 20° C. or lower, more preferably in a range of 5 to 10° C.

As described in the above, with the use of the IMC method according tothe fifth aspect of the present invention, it becomes possible to employa temperature of the mold lower than a curing temperature of a coatingmaterial by virtue of the effective utilization of heat held in athermoplastic resin molded product. In this way, it is allowed to reducea time period necessary for heating and cooling the mold, therebyaccelerating the molding cycle and thus improving the productivity.Further, since the curing temperature of a coating material can be usedto maintain some predetermined conditions, it is sure for a formedcoating layer to obtain good physical properties.

BEST MODEL FOR CARRYING OUT THE INVENTION Examples

In the following, the present invention will be described in more detailby giving out some examples. However, the present invention should notbe limited in its scope to any extent by these examples.

Example 1

A mold having a shear edge structure was used which is capable ofproducing a case-like product having a height of 300 mm, a width of 210mm, a depth of 50 mm and a thickness of 3 mm. A thermal resistant ABSresin (commercially available under a trade name “CYCOLAC MX40”,manufactured by Ube Cycon. Ltd.) was injection-molded by applying aforce of 200 tons as a mold closing force. At this time, the temperatureof the resin was 250° C., while the temperature of the mold was 90° C. Acooling time used in the resin molding process was 20 seconds. At thismoment, the surface temperature of the thermoplastic resin moldedproduct was about 100° C. Afterwards, the mold was opened by 1.5 mm, 12cc of coating material A having a gel time of 7 seconds at a temperatureof 90° C., as listed in Table 2 was injected under a pressure of 12 MPa.2.5 Seconds were required in the injection of the coating material. 0.1Second after the injection of the coating material, the mold began to beclosed again, by applying a mold closing force not larger than 20 tonswithin one second. Then, after the mold had been kept in position for120 seconds, the mold was opened and molded product was taken out. Itwas found that thus molded product had been covered up by a uniformlyformed coating layer having a thickness of 100 μm, but without havingany mottles, wrinkles and cracks thereon.

Example 2

A mold used in Example 1 was used. Then, in the same manner as inExample 1, an amount of polyamide resin (commercially available under atrade name “UBE NYLON PA1013B”, manufactured by Ube Industries, Ltd.)was injection-molded by applying a force of 300 tons as a mold closingforce. At this time, the temperature of the resin was 250° C., while thetemperature of the mold was 120° C. A cooling time used in the resinmolding process was 20 seconds. At this moment, the surface temperatureof the thermoplastic resin molded product was about 140° C. Afterwards,the mold was opened by 1.5 mm, 12 cc of coating material B having a geltime of 8 seconds at a temperature of 120° C., as listed in Table 2 wasinjected under a pressure of 11 MPa. Two seconds were required in theinjection of the coating material. Three seconds after the injection ofthe coating material, the mold began to be closed again, by applying amold closing force not larger than 20 tons within 3 seconds. Then, afterthe mold had been kept in position for 120 seconds, the mold was openedand molded product was taken out. It was found that thus molded producthad been covered up by a uniformly formed coating layer having athickness of 100 μm, but without having any weld line of an aluminumflake pigment, its orientation irregularities, wrinkles and cracks.

Comparative Example 1

The same mold, resin to be used for molding and coating material as usedin Example 1 were used in this comparative example. The time requiredfor from the start of the reclosing of the mold to the completion of thereclosing of the mold after the completion of injecting the coatingmaterial was set at 5.5 seconds. The molding was carried out under thesame conditions as in Example 1 except for those mentioned above. It wasfound that a coated resin product thus obtained has wrinkles and blackstripe-like color irregularities formed along the flow path of thecoating material. As a result, molded product having a uniform coatinglayer could not be obtained.

Comparative Example 2

The same mold, resin to be used for molding and coating material as usedin Example 2 were used in this comparative example. The time for theinjection of the coating material was set at 0.5 seconds. The moldingwas carried out under the same conditions as in Example 2 except forthose mentioned above. It was found that a coated resin product thusobtained has weld lines made of aluminum flake orientationirregularities and color irregularities caused due to a color pigment.As a result, molded product having a uniform coating layer could not beobtained.

TABLE 2 Coating materials Components A B Urethane acrylate oligomer (1)100.0 50.0 Urethane acrylate oligomer (2) — 50.0 Tripropylene glycoldiacrylate 57.0 30.0 Styrene 3.0 30.0 Titanium oxide 150.0 — Carbonblack 0.1 — Aluminum pigment (1) — 0.2 Aluminum pigment (2) — 0.8Urethane acrylate oligomer (1) 1.7 1.6 Zinc stearate — 1.6 Photostabilizer TINUVIN 1130 — 0.8 8% cobalt octoate 0.5 0.2Bis(4-t-butylcyclohexyl) peroxy carbonate 2.5 —t-almyl-peroxy-2-ethylhexanoate — 2.0 Urethane acrylate oligomer (1)Molecular weight: 2,500 Urethane acrylate oligomer (2) Molecular weight:6,500 Aluminum pigment (1) Average particle diameter: 30 μm Aspectratio: 30 Aluminum pigment (2) Average particle diameter: 25 μm Aspectratio: 2 Tinuvin: registered trademark of Ciba-Geigy Co., Ltd.

Example 3

FIG. 4( a) shows a flow chart for the molding steps of Example 3 under acondition described later in detail by using an IMC apparatus 100 shownin FIG. 1. FIG. 4( b) shows a sequence for mold closing and opening. Amold having a shear edge structure was used which is capable ofproducing a case-like product having a height of 300 mm, a width of 210mm, a depth of 50 mm. Firstly, a Nylon 6 (commercially available underthe trade name “UBE NYLON PA1013B”, manufactured by Ube Industries.Ltd.) was injection-molded by applying a force of 350 tons as a moldclosing force. At this time, the temperature of the resin was 250° C.,while the temperature of the mold was 130° C.

Thirty seconds was spent as a cooling time for the molded resin.Afterwards, the mold was opened by 0.5 mm. Then, the mold was kept atsuch an opened position for 10 seconds. Afterwards, 13 cc of coatingmaterial having a good adhesiveness to Nylon 6 and having a gel time of8 seconds at a temperature of 130° C. was injected into a space formedbetween the thermoplastic resin molded product and the internal surfaceof the mold. Two seconds were spent for the injection of the coatingmaterial. Three seconds after the injection of the coating material, themold began to be closed again, with applying a mold closing force of 100tons for one second. Approximately 1.0 second was required to increase apressure as desired (increase a mold closing force). Subsequently,another mold closing force for a second mold closure step was appliedwithin a time period of 50 seconds in a manner such that a coatingmaterial pressure sensor would arrive at its predetermined pressurevalue of 3.0 MPa. After that, a further mold closing force for a thirdmold closure step was applied within a time period of 50 seconds in amanner such that a coating material pressure sensor would arrive at itspredetermined pressure value of 2.0 MPa.

A finally obtained molded product was found to have been completelycovered by a coating layer having a thickness of 100 μm. As proved inthis example, if a pressure within the mold after the injection of acoating material is caused to change in such a manner that said pressureis high immediately after the coating material injection and then dropsgradually, the coating material can more uniformly spread within themold. Further, since it is also allowed to use a coating material havinga high viscosity, a selectable rang for selecting a usable coatingmaterial has become broader than before.

However, an adhesion strength of a coating layer when it adheres to anintegrally molded product was evaluated in a test called lattice patterncellophane tape test prescribed in JIS K-5400 (General Testing Methodfor Coating Material). As a result, no peeling-off was found in thecoating layer in 100 lattices of the lattice pattern, thereby provingthat the obtained coating layer has a high adhesion strength.

Example 4

FIG. 5 shows a flow chart indicating a molding process for use in thisexample under a condition described later by using an IMC apparatus 100shown in FIG. 1. Furthermore, a sequence for mold opening was the sameas that shown in FIG. 3.

In detail, a mold having a shear edge structure was used which iscapable of producing a case-like product having a height of 300 mm, awidth of 210 mm, a depth of 50 mm. At first, a thermal resistant resin(commercially available under a trade name “MX40”, manufactured by UbeIndustries. Ltd.) was injection-molded under the application of a forceof 350 tons as a mold closing force. At this time, the temperature ofthe resin was 250° C., while the temperature of the mold was 90° C.

Thirty seconds were spent as a cooling time for the molded resin.Afterwards, the mold was opened by 1.0 mm. Subsequently, 13 cc ofcoating material having a good adhesiveness to an ABS resin and having agel time of 7 seconds at a temperature of 90° C. was injected into aspace formed between the thermoplastic resin molded product and theinternal surface of the mold. Two seconds were needed in the injectionof the coating material. Soon after the injection of the coatingmaterial, the mold was closed rapidly. At this time, about 1.5 secondswere needed in increasing the mold closing force. The mold closing forcewas set at only one step. Such a mold closing force was applied during120 seconds in a manner such that a coating material pressure sensorwould arrive at its predetermined pressure value of 3.0 MPa.

A finally obtained molded product was found to have been completelycovered by a coating layer having a thickness of 100 μm. The moldedproduct has formed thereon a coating layer whose thickness uniformitywas just as good as that in Example 3. Therefore, it is understood thatfor some kinds of coating materials it is not necessary to use amulti-stage mold closing force. Further, similar to Example 3, anadhesion strength of a coating layer when it adheres to an integrallymolded product was evaluated in a test called lattice pattern cellophanetape test prescribed in JIS K-5400 (General Testing Method for CoatingMaterial). As a result, no peeling-off was found in the coating layer in100 lattices of the lattice pattern, thereby proving that the obtainedcoating layer has a high adhesion strength.

Example 5

FIG. 6 shows a flow chart indicating a molding process for use in thisexample under a condition described later by using the IMC apparatusshown 100 in FIG. 1. Moreover, a sequence for mold opening was the sameas that shown in FIG. 3.

In detail, a mold of a flat parting type was used which is capable ofproducing a generally triangular product which can serve as a side coverfor use in a motor bike, having a height of 320 mm and a width of 180mm. At first, a thermal resistant ABS resin (commercially availableunder a trade name “MX40”, manufactured by Ube Cycon. Ltd.) wasinjection-molded by applying a force of 300 tons as a mold closingforce. Here, a rib for preventing the leakage of a coating material wasformed along the entire circumference of the mold, a resin molding gateis provided on a surface which is just opposite to the coating materialinjection surface. At this time, the temperature of the resin was 250°C., while the temperature of the mold was 90° C.

Thirty seconds were spent as a cooling time the molded resin.Afterwards, the mold was opened by 1.0 mm. Subsequently, 4 cc of coatingmaterial having a good adhesiveness to ABS resin and having a gel timeof 7 seconds at a temperature of 90° C. was injected into a space formedbetween the thermoplastic resin molded product and the internal surfaceof the mold. One second was needed in the injection of the coatingmaterial. Soon after the injection of the coating material, the mold wasclosed rapidly. At this time, about 0.8 seconds were needed inincreasing the mold closing force. The mold closing force was set atonly one step. Such a mold closing force was applied during 120 secondsin a manner such that a coating material pressure sensor would arrive atits predetermined pressure value of 3.0 MPa.

A finally obtained molded product was found to have been completelycovered by a coating layer having a thickness of 100 μm. Further,similar to Examples 3 and 4, an adhesion strength of a coating layerwhen it adheres to an integrally molded product was evaluated. As aresult, no peeling-off was found in the coating layer in 100 lattices ofthe lattice pattern, thereby proving that the obtained coating layer hasa high adhesion strength. Further, as indicated by the results of thisexample, if a feedback control is conducted using a coating materialpressure sensor, the IMC method for dealing with a thermoplastic resinusing a flat parting type mold can be carried out without anydifficulty.

Example 6 and Comparative Example 3

A mold having a shear edge structure was used which is capable ofproducing a case-like product having a height of 300 mm, a width of 210mm, a depth of 50 mm. Such a mold was equipped with a coating materialinjection device capable injecting a predetermined amount of a coatingmaterial. An injection molding machine of 350 tons was used which is atoggle mold closing type, capable of optionally changing the moldclosing force. After ABS resin was injection-molded, a coating materialconsisting of components listed in Table 3 and having a gel time of 7seconds was injected into the mold cavity, thereby forming a coatinglayer on the surface of a thermoplastic resin molded product. Althoughmolding conditions in this example are substantially the same as thoseused in other examples, this example employed a mold shown in FIG. 9 andalso used a heater (not shown) to perform a predetermined heatingtreatment so that the temperature of the heating block 132 was elevatedto 120° C., while other portions of the mold were kept at 90° C.

TABLE 3 Weight percent Components (%) Urethane acrylate oligomer *1 16.0Epoxy acrylate oligomer *2 16.0 Styrene 22.0 Zinc stearate 0.3 Titaniumdioxide 45.0 Carbon black 0.1 8% cobalt octoate 0.6t-butylperoxy-2-ethylhexanoate 1.0 *1 Urethane acrylate oligomer:molecular weight; 2,500 *2 Epoxy acrylate oligomer: molecular weight;540

Here, the general structure of a mold formed according to Example 6 isas shown in FIG. 9. An IMC mold 150 is comprised of a fixed mold portion51 and a movable mold portion 52. The fixed mold portion 51 includes asprue portion 154 for injecting an amount of resin, a coating materialinjection device 55 for injecting a coating material, and a heatingblock 132. The movable mold portion 52 has been processed into astructure containing an auxiliary cavity 7. In fact, the mold has beenformed into a structure which ensures that an auxiliary molded body 44will be integrally formed with a molded product 43 formed in the moldcavity.

The auxiliary cavity 7 is formed as having a length of 10 mm, athickness of 0.3 mm, so that it is communicated with the mold cavity andextends along the entire circumference thereof. However, as will bediscussed later in the present specification, the auxiliary cavity 7 isformed at its corner with a portion having a thickness which is at most0.6 mm, thereby making it possible to avoid a problem possibly causeddue to an insufficiency in process precision. Further, the precision ofthe length of the auxiliary cavity 7 was controlled within a range of±0.2 mm.

On the other hand, a mold 160 used in Comparative Example 3 is as shownin FIG. 10. Its fixed mold portion 51 is just the same as the fixed moldportion 51 of the IMC mold 150 shown in FIG. 9. However, its movablemold portion 52 has a shear edge portion which is just the same as aconventional one, while the mold as a whole does not have an auxiliarycavity.

In the Comparative Example 3, molded products were made in the sameconditions as used in Example 6, except that a mold used is an IMC mold160 not having an auxiliary cavity. Namely, the temperature of a heatingblock 132 is set to be 120° C., while other portions of the mold werekept at a temperature of 90° C.

After the coating material has been cured, the mold was opened and themolded product was taken out. The molded product thus obtained waschecked to investigate how the coating material was flowing within themold and whether the coating material had leaked out of the mold.

FIG. 11 is an explanatory view indicating a molded product made with theuse of the IMC mold 50 which is formed according to the fourth aspect ofthe present invention. A cross section B in the figure represents asection on one side surface of the molded product 40, providing anenlarged view indicating how the coating layer 42 was formed on thecorner portion of the mold. In fact, the molded product 40 is comprisedof a resin molded portion 41 and a coating layer portion 42. The resinmolded portion 41 includes a molded product main body 43 and anauxiliary molded portion 44. As shown in FIG. 11, the coating materialwas stopped in the auxiliary molded portion 44 of the molded product 40,without any leakage of the coating material to the outside of the mold.Further, the corner portion of the auxiliary molded portion 44 has athickness of 0.6 mm, allowing a deeper flow of the coating material thanother portions of the molded product, but preventing the coatingmaterial from flowing out of the mold.

However, when the IMC mold 150 was used which was formed according tothe fourth aspect of the present invention, and when a molded productwas manufactured under a condition where the temperature of the heatingblock 132 was set at 90° C. which is the same temperature as those ofother portions of the mold, it was found that the coating material hadleaked only in part of the corner portion where the auxiliary moldedportion was thick. Accordingly, in order to ensure a high precision informing an auxiliary cavity, if an auxiliary cavity has an undesirablylarge thickness, a necessary treatment for preventing any possibletrouble is only to make longer the length of the auxiliary cavity tosuch an extent that any possible leakage of a coating material may beeffectively prevented. In addition, it can be understood that if anauxiliary cavity has been formed with a satisfactory precision, theprovision of a heating block is no longer necessary.

On the other hand, when an IMC mold 160 was used which belongs to aconventional type as used in the Comparative Example 3, even if thetemperature of the heating block 132 was set at 120° C., the coatingmaterial was found to have leaked from the shear edge portion. As aresult, it was necessary to wipe off the leaked coating material. Thus,by analyzing the test results obtained in the test where the IMC mold150 was used and the temperature of the heating block 132 was changed,it can be expected that if the IMC mold 160 used in the ComparativeExample 3 is employed and if the temperature of the heating block 132 isset at 90° C. which is the same temperature as those of other portionsof the mold, there would be too much a leakage of a coating materialthan the case in which the heating block 132 is set at a temperature of120° C. Further, such kind of coating material leakage was actuallyconfirmed by the experiment.

Comparative Example 4

A mold having a shear edge structure was used which is capable ofproducing a case-like product 71 having a height of 300 mm, a width of210 mm and a depth of 50 mm, as shown in FIG. 15( b). An injectionmolding machine used was 350-ton injection molding apparatus capable ofoptionally changing its mold closing force. Also, an injection devicewas used which is capable of injecting a necessary amount of coatingmaterial. A coating material including the components listed in Table 4and having a gel time of 7 seconds, was injected into the mold, followedby changing the internal pressure within the mold. Then, the hump sizeof the molded product, an adhesion strength between the coating materialand the molded product were all investigated.

TABLE 4 Weight percent Components (%) Urethane acrylate oligomer *1 16.0Epoxy acrylate oligomer *2 16.0 Styrene 22.0 Zinc stearate 0.3 Titaniumdioxide 45.0 Carbon black 0.1 8% cobalt octoate 0.6t-butylperoxy-2-ethylhexanoate 1.0 *1 Urethane acrylate oligomer:molecular weight; 2,500 *2 Epoxy acrylate oligomer: molecular weight;540

FIG. 15( a) is an explanatory view indicating a pressure applyingpattern of an IMC method used in the present comparative example. Atfirst, a mold having a shear edge structure was used which is capable ofproducing a case-like product as shown in FIG. 15( b). Then, a moldclosing force of 350 tons was applied and an amount of usual grade Nylon6 (commercially available under a trade name “UBE NYLON 1013B”,manufactured by Ube Industries. Ltd.) was injection molded, therebyforming a molded product 71. However, as shown in FIG. 15( b), thebottom of the molded product 71 has been processed into a configurationincluding ribs 91 (each having a thickness of 3 mm) and ribs 92 (eachhaving a thickness of 5 mm). In FIG. 15( b), a reference numeral 72represents an opening for injecting a coating material.

After the molded product 71 was formed, the mold was opened by 1 mm, sothat a coating material for forming a desired coating layer wasinjected. At this time, the temperature of the mold was 120° C. Upon thecompletion of the injection of the coating material, the mold closingforce was rapidly increased and was then kept at this state for onesecond. Subsequently, the mold closing force was reduced rapidly. Atthis moment, about 2 seconds were needed in a process from the start ofincreasing the mold closing force until the arrival of a low moldclosing force. Since the mold closing force in the mold is all appliedto the projection plane of the molded product, an in-mold pressure willbe a value obtainable by dividing the mold closing force with theprojected area.

In the present comparative example, as shown in FIG. 15( a), a moldclosing force at a time of zone D (high pressure applying zone) and amold closing force at a time of zone E (low pressure maintaining zone)were changed so as to change the in-mold pressure. The molded product 71obtained under such a condition was checked to investigate whether andto what extent some humps (tubercles on the surface of the moldedproduct) had occurred in the vicinity of the ribs 91 and ribs 92, alsoto investigate an adhesion strength of the formed coating layer. Here,humps were investigated by measuring the size of tubercles in thevicinity of ribs each having a width of 3 mm, with the use of a contourshape measuring device manufactured by Tokyo Seimitsu Co., Ltd.Tubercles having a size of 10 μm or larger are represented by “x”, thosehaving a size less than 10 μm are represented by “◯”. Further, theadhesion strength of each coating layer was evaluated in a test calledlattice pattern cellophane tape test prescribed in JIS K-5400 (GeneralTesting Method for Coating Material). Here, “x” represents a case whereat least one peeling-off was found in the coating layer in 100 latticesof the lattice pattern, “◯” represents a case where not even onepeeling-off was found in the coating layer in 100 lattices of thelattice pattern. The test results are shown in Table 5.

TABLE 5 Measured results of in-mold pressure, hump and adhesion strengthAdhesion Adhesion Pressure Pressure strength strength Sample in zone Din zone E (central (Peripheral No. (MPa) (MPa) Hump portion) portions) 110.0 10.0 ∘ ∘ x 2 8.0 8.0 ∘ ∘ x 3 5.0 5.0 ∘ ∘ x 4 3.0 3.0 x x x 5 — 2.0x x x 6 1.0 1.0 x x x 7 0.5 0.5 x x x 8 10.0 1.0 ∘ ∘ x 9 5.0 0.5 ∘ ∘ x

In Table 5, a pressure in zone D means an in-mold pressure at a time ofzone D (high pressure applying zone) shown in FIG. 15( a), a pressure inzone E means an in-mold pressure at a time of zone E (low pressuremaintaining zone) shown in FIG. 15( a). Further, as to the results of anadhesion strength test, a central portion adhesion strength means a testresult obtained by measuring an adhesion strength in the vicinity (referto FIG. 15( b)) of the center of the bottom of the molded product,whereas a peripheral portion adhesion strength means a test resultobtained by measuring an adhesion strength in the vicinity (refer toFIG. 15( b)) of a vertical surface of the bottom of the molded product.Further, in the present comparative example, the adhesion strength ofeach coating layer, as in the cases of sample numbers 1 to 3, 8 and 9,when a pressure in zone D was 5.0 MPa or higher, the central portiongave relatively good test results while the peripheral portions gaveonly bad test results. Further, as in the cases of sample numbers 4 to7, when a pressure in zone D was less than 5.0 MPa, the central portionfailed to give relatively good adhesion strength.

The above results may be explained as follows. Namely, in a mold havingthe shear edge structure, it is impossible to completely prevent theleakage of a coating material. As a result, the in-mold pressure willbecome high in the central portion, but will become low in theperipheral portions. However, it is understood that a high pressure inzone D will be useful for avoiding the occurrence of humps.

Example 7

A flat parting type mold was used which has parting surfaces and hasribs for preventing coating material leakage around the entirecircumference of a molded product 73, as shown in FIG. 15( c). Such amold was capable of producing a generally triangular molded product 73having a height of 320 mm and a width of 180 mm, having a configurationof a side cover for use in a motor bike. Here, an injection moldingmachine, an injection device and a coating material, which are all thesame as those used in the above comparative example, were employed inthis Example. In fact, an in-mold pressure after the injection of acoating material was changed, thereby obtaining a desired molded productcoated with a coating layer. Finally, the humps of each molded productwere checked, an adhesion strength of each coating layer was alsoinvestigated.

The molding process was conducted in the same manner as in ComparativeExample 4. At first, an amount of standard Nylon 6 (commerciallyavailable under the trade name “UBE NYLON 1013B”, manufactured by UbeIndustries. Ltd.) was injection molded in an injection molding machine.Then, the mold was opened so as to form a gap of 1 mm, and an amount ofcoating material having a gel time of 7 seconds (listed in Table 4) wasinjected into the gap. Subsequently, a mold closing force was appliedwithin one second so that the in-mold pressure would arrive at a valueas shown in Table 6. Once the coating material had spread over theentire molded product within the mold, the mold closing force wasrapidly reduced. At this time, an in-mold pressure was not a valuecalculated from the mold closing force, but a value directly measuredwith the use of an ejector pin. After the coating material had beencured for 120 seconds, the molded product was taken out from the mold.The humps and the adhesion strength were measured in the same manner asin the above comparative example. The results of this example are listedin Table 6.

TABLE 6 Measured results of in-mold pressure, hump and adhesion strengthAdhesion Adhesion Pressure Pressure strength strength Sample in zone Din zone E (central (Peripheral No. (MPa) (MPa) Hump portion) portions)10 10.0 3.0 x ∘ ∘ 11 10.0 1.0 ∘ ∘ ∘ 12 10.0 0.5 ∘ ∘ ∘ 13 3.0 1.0 ∘ x x14 2.0 1.0 ∘ x x

In Table 6, a pressure in zone D means an in-mold pressure at a time ofzone D (high pressure applying zone) shown in FIG. 15( a), a pressure inzone E means an in-mold pressure at a time of zone E (low pressuremaintaining zone) shown in FIG. 15( a). Further, as to the results of anadhesion strength test, a central portion adhesion strength means a testresult obtained by measuring an adhesion strength in the vicinity (referto FIG. 15( b)) of the center of the bottom of the molded product,whereas a peripheral portion adhesion strength means a test resultobtained by measuring an adhesion strength in the vicinity (refer toFIG. 15( b)) of a vertical surface of the bottom of the molded product.However, it is understood that since the mold used in this example has astructure of preventing the leakage of a coating material, an internalpressure in the peripheral portions of the molded product was the sameat that in the central portion thereof. Accordingly, as in the cases ofsample numbers 11 and 12, if a pressure in zone D is kept at asufficiently high level while a pressure in zone E is kept at a lowvalue, it is possible to prevent the occurrence of humps, therebyensuring a relatively high adhesion strength for the entire product. Onthe other hand, in the case of sample number 10, some humps had occurreddue to a high pressure in zone E. Moreover, in the cases of samplenumbers 13 and 14, we were not be able to obtain a good adhesionstrength because a pressure in zone D was low.

Example 8

FIG. 16 shows a flow chart and a sequence for mold closing and moldopening, which are designed to carry out Example 8 using the IMCapparatus shown in FIG. 1. In this example, a mold having a shear edgestructure was used which is capable of producing a case-like producthaving a height of 300 mm, a width of 210 mm, a depth of 50 mm and athickness of 3 mm. Then, a mold closing force of 200 tons was applied toinjection mold an amount of heat resistant ABS resin (commerciallyavailable under a trade name MX40, manufactured by Ube Cycon., Ltd.). Atthis time, the temperature of the resin was 250° C., while thetemperature of the mold cavity of the mold was 90° C. Then, 30 secondswere needed in a cooling step involved in the resin molding process.When the surface temperature of the thermoplastic resin molded productarrived at 100° C., the mold was opened by 1 mm and kept at thatposition for 10 seconds. After that, 13 cc of a coating material listedin Table 7 was injected into the mold within a time period of 2 seconds.At this time, it was understood that the coating material was at atemperature of 100° C. and would be cured within one minute. Uponcompletion of the injection of the coating material, the mold was closedagain with a mold closing force of 50 tons. After being kept at thatposition for 120 seconds, the mold was opened and an integrally formedproduct was taken out.

The integrally formed product has a coating layer of 100 μm formed overthe entire surface thereof. An adhesion strength of the coating layerwhen it adheres to an integrally molded product was evaluated in a testcalled lattice pattern cellophane tape test prescribed in JIS K-5400(General Testing Method for Coating Material). As a result, nopeeling-off was found in the coating layer in 100 lattices of thelattice pattern, thereby proving that the obtained coating layer has ahigh adhesion strength.

In this example, an amount of internal heat within the molded resinproduct can be effectively used in the curing of a coating material, andit is possible to set the temperature of the mold at a low value. Inthis way, the mold temperature may be set lower than the curingtemperature of a coating material, making it possible to shorten themanufacturing time period for one cycle of molding formation. Therefore,it is sure to continuously improve the productivity and to cure acoating material under a predetermined condition, thereby making itpossible for a coating layer to obtain desired and predeterminedcharacteristics.

TABLE 7 Components of coating material A Weight percent Urethaneacrylate oligomer 100.0 1,6-hexan diol diacrylate 65.0 8% cobalt octoate0.2 Zinc stearate 1.6 Titanium dioxide 150.0 Carbon black 0.1Bis-(4-t-butyl cyclohexyl) peroxy Carbonate 3.0 *1 Urethane acrylateoligomer: Molecular weight; 2,500

INDUSTRIAL APPLICABILITY

In the in-mold coating formation method according to the first aspect ofthe present invention, since a time necessary for injecting a coatingmaterial and a time period from the beginning of injection of thecoating material until the ending of a mold reclosing step can be set inaccordance with a gel time of the coating material, it has becomepossible to effectively manufacture a coated product having a uniformquality in its outside appearance, whose cured coating layer is freefrom any defects such as pigment separation, weld lines, wrinkles andcracks.

In using the in-mold coating formation method and the in-mold coatingformation apparatus according to the second aspect of the presentinvention, since the mold position and the mold closing force can all becontrolled by the stroke pattern of the mold closing cylinder and can besubjected to a feedback control, it is possible to perform a continuouscontrol without having to change a control object. Further, with the useof a toggle type injection molding machine, it is possible to controlthe position of the mold with a high speed and a high precision. In thisway, it is sure to obtain a simplified control system and a highresponse capable of dealing with a sudden change in an operationpattern.

Further, according to this aspect of the present invention, byperforming a feedback control in accordance with a predetermined coatingmaterial pressure pattern, even if an in-mold coating formation will bedifferent from one shot to another, it is still possible for eachcoating layer to obtain a stabilized outside appearance and a stabilizedadhesion strength. Moreover, with the use of a shear edge type moldwhich was often used to deal with SMC and BMC, even if only a feedbackcontrol of the mold closing force is performed without performing anyother controls, it is still possible to obtain an integrally formedmolded product coated with a coating layer having a sufficiently uniformand high adhesion strength.

Further, with the use of the in-mold coating formation mold and thein-mold coating formation method involving the use of such a mold,according to the third aspect of the present invention, since a coatingmaterial may be prevented from leaking to the outside of the mold, themolding formation cycle may be stabilized, thereby improving theproductivity and maintaining product quality at a stabilized level. Thiseffect is extremely larger than a minus effect caused due to anincreased step of removing an auxiliary molded portion integrally formedwith the molded resin main body.

Moreover, with the use of the in-mold coating formation method accordingto the fourth aspect of the present invention, since the coatingmaterial leakage from the mold cavity can be prevented and the in-moldpressure can be kept uniform with respect to the entire molded productand the entire coating layer, it is sure to obtain an integrally formedmolded product coated with a layer having a sufficient adhesionstrength. Further, by controlling a pressure applying pattern under apredetermined condition, the thickness of a coating layer may becontrolled at a constant value, thereby effectively inhibiting theformation of humps on thick portions such as rib areas of the moldedproduct. Moreover, with the use of the present invention, even if acoating material is a commonly used coating material and a molding resinis a usual grade resin, it is still possible to obtain a molded resinproduct coated with a coating layer having a sufficient adhesionstrength. Therefore, it is allowed to save a lot of time and to avoidunnecessary expense which are otherwise needed for developing specialcoating material and special grade resin. In conclusion, with the use ofthe fourth aspect of the present invention, by employing only usualcoating materials and usual resin to be used for moldings, it is sure toreduce the occurrence of defect products, increase the productionefficiency, thereby improving the reliability and reducing theproduction cost.

In addition, with the use of the in-mold coating formation methodaccording to the fifth aspect of the present invention, since it isallowed to effectively use an amount of heat held within a moldedproduct, the temperature of the mold may be set at a value which islower than the curing temperature of a coating material. As a result, itpossible to shorten the molding formation cycle, thereby greatlyimproving the productivity. Meanwhile, since the curing process of acoating material may be carried out under a predetermined temperaturecondition which is higher than the temperature of the mold, it ispossible for a coating layer to obtain desired characteristics. Further,if the temperature of a mold is set at the same value as in a prior art,it will be allowed to use a coating material having a higher curingtemperature. In this way, a selectable range for selecting a coatingmaterial has become broader than before, making it possible to usevarious coating materials having an excellent heat resistance andweather resistance.

Therefore, with the use of the present invention, it has become possibleto produce highly reliable products with a higher efficiency and a lowercost as compared with conventional methods.

1. An in-mold coating formation mold which is equipped with a coatingmaterial injection device for injecting a coating material into a moldcavity in order that a coating layer can be formed on the surface of athermoplastic resin molded product within the mold, comprising: a malemold and female mold, defining the mold cavity, with parting surfacesthat can be in a contacted position; and an auxiliary cavity, whichextends in the opening and closing direction of the mold, begins at theparting surfaces of the male and female molds, ends at the beginning ofthe mold cavity formed between the male and female molds, and has athickness of 0.1 mm to 2 mm and a length of 0.5 mm to 30 mm capable ofreceiving a molten resin; wherein an auxiliary molded body is formed insaid auxiliary cavity at the time of injection of the molten resin intothe cavity, and wherein said auxiliary cavity is formed in such a mannerthat it communicates with the mold cavity, through an entirecircumference thereof, and the auxiliary cavity having an end at a sideopposite to the mold cavity and being formed such that the auxiliarycavity prevents the entry of molten resin in between the partingsurfaces of both male and female molds, the parting surfaces contacteach other at the end of the auxiliary cavity during molding of themolded product and remain in contact during reopening of the male andfemale molds for charging the coating material, whereby leakage ofcoating material can be prevented because a gap, formed when theauxiliary molded body in the auxiliary cavity shrinks in the thicknessdirection, is not large enough to allow the coating material to leak outof the mold.
 2. An in-mold coating formation mold according to claim 1,wherein there is provided a heater for heating a cavity surface of theauxiliary cavity, said cavity surface being on the coating materialinjection side.